Ship the required macros in the m4/ directory.

This is recommended practice as per
https://www.gnu.org/software/automake/manual/html_node/Local-Macros.html.

It fixes the problem that arose when one of the maintainers could not build LibVNCServer
after https://github.com/LibVNC/libvncserver/pull/38 was merged.

Symptoms included

  checking whether make sets $(MAKE)... yes
  ./configure: line 2481: syntax error near unexpected token `rfb/rfbconfig.h'
  ./configure: line 2481: `AX_PREFIX_CONFIG_H(rfb/rfbconfig.h)'

until autoconf-archive was installed (which was a previously unmentioned
requirement for Pull Request #38) – this is not always an option, in particular
when the project needs to be built using a system-wide autoconf installation
that cannot be modified easily by the developer.

m4/ax_prefix_config_h.m4

+# ===========================================================================
+#    http://www.gnu.org/software/autoconf-archive/ax_prefix_config_h.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_PREFIX_CONFIG_H [(OUTPUT-HEADER [,PREFIX [,ORIG-HEADER]])]
+#
+# DESCRIPTION
+#
+#   Generate an installable config.h.
+#
+#   A package should not normally install its config.h as a system header,
+#   but if it must, this macro can be used to avoid namespace pollution by
+#   making a copy of config.h with a prefix added to all the macro names.
+#
+#   Each "#define SOMEDEF" line of the configuration header has the given
+#   prefix added, in the same case as the first character of the macro name.
+#
+#   Defaults:
+#
+#     OUTPUT-HEADER = $PACKAGE-config.h
+#     PREFIX = $PACKAGE
+#     ORIG-HEADER, from AM_CONFIG_HEADER(config.h)
+#
+#   Your configure.ac script should contain both macros in this order.
+#
+#   Example:
+#
+#     AC_INIT(config.h.in)        # config.h.in as created by "autoheader"
+#     AM_INIT_AUTOMAKE(testpkg, 0.1.1)    # makes #undef VERSION and PACKAGE
+#     AM_CONFIG_HEADER(config.h)          # prep config.h from config.h.in
+#     AX_PREFIX_CONFIG_H(mylib/_config.h) # prep mylib/_config.h from it..
+#     AC_MEMORY_H                         # makes "#undef NEED_MEMORY_H"
+#     AC_C_CONST_H                        # makes "#undef const"
+#     AC_OUTPUT(Makefile)                 # creates the "config.h" now
+#                                         # and also mylib/_config.h
+#
+#   If the argument to AX_PREFIX_CONFIG_H would have been omitted then the
+#   default output file would have been called simply "testpkg-config.h",
+#   but even under the name "mylib/_config.h" it contains prefix-defines
+#   like
+#
+#     #ifndef TESTPKG_VERSION
+#     #define TESTPKG_VERSION "0.1.1"
+#     #endif
+#     #ifndef TESTPKG_NEED_MEMORY_H
+#     #define TESTPKG_NEED_MEMORY_H 1
+#     #endif
+#     #ifndef _testpkg_const
+#     #define _testpkg_const _const
+#     #endif
+#
+#   and this "mylib/_config.h" can be installed along with other header
+#   files, which is most convenient when creating a shared library (that has
+#   some headers) whose functionality depends on features detected at
+#   compile-time. No need to invent some "mylib-confdefs.h.in" manually.
+#
+#   Note that some AC_DEFINEs that end up in the config.h file are actually
+#   self-referential - e.g. AC_C_INLINE, AC_C_CONST, and the AC_TYPE_OFF_T
+#   say that they "will define inline|const|off_t if the system does not do
+#   it by itself". You might want to clean up about these - consider an
+#   extra mylib/conf.h that reads something like:
+#
+#     #include <mylib/_config.h>
+#     #ifndef _testpkg_const
+#     #define _testpkg_const const
+#     #endif
+#
+#   and then start using _testpkg_const in the header files. That is also a
+#   good thing to differentiate whether some library-user has starting to
+#   take up with a different compiler, so perhaps it could read something
+#   like this:
+#
+#     #ifdef _MSC_VER
+#     #include <mylib/_msvc.h>
+#     #else
+#     #include <mylib/_config.h>
+#     #endif
+#     #ifndef _testpkg_const
+#     #define _testpkg_const const
+#     #endif
+#
+# LICENSE
+#
+#   Copyright (c) 2014 Reuben Thomas <rrt@sc3d.org>
+#   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+#   Copyright (c) 2008 Marten Svantesson
+#   Copyright (c) 2008 Gerald Point <Gerald.Point@labri.fr>
+#
+#   This program is free software; you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation; either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 15
+
+AC_DEFUN([AX_PREFIX_CONFIG_H],[dnl
+AC_PREREQ([2.62])
+AC_BEFORE([AC_CONFIG_HEADERS],[$0])dnl
+AC_CONFIG_COMMANDS(m4_default([$1], [$PACKAGE-config.h]),[dnl
+AS_VAR_PUSHDEF([_OUT],[ac_prefix_conf_OUT])dnl
+AS_VAR_PUSHDEF([_DEF],[ac_prefix_conf_DEF])dnl
+AS_VAR_PUSHDEF([_PKG],[ac_prefix_conf_PKG])dnl
+AS_VAR_PUSHDEF([_LOW],[ac_prefix_conf_LOW])dnl
+AS_VAR_PUSHDEF([_UPP],[ac_prefix_conf_UPP])dnl
+AS_VAR_PUSHDEF([_INP],[ac_prefix_conf_INP])dnl
+m4_pushdef([_script],[conftest.prefix])dnl
+m4_pushdef([_symbol],[m4_cr_Letters[]m4_cr_digits[]_])dnl
+_OUT=`echo m4_default([$1], [$PACKAGE-config.h])`
+_DEF=`echo _$_OUT | sed -e "y:m4_cr_letters:m4_cr_LETTERS[]:" -e "s/@<:@^m4_cr_Letters@:>@/_/g"`
+_PKG=`echo m4_default([$2], [$PACKAGE])`
+_LOW=`echo _$_PKG | sed -e "y:m4_cr_LETTERS-:m4_cr_letters[]_:"`
+_UPP=`echo $_PKG | sed -e "y:m4_cr_letters-:m4_cr_LETTERS[]_:"  -e "/^@<:@m4_cr_digits@:>@/s/^/_/"`
+_INP=`echo "$3" | sed -e 's/ *//'`
+if test ".$_INP" = "."; then
+   for ac_file in : $CONFIG_HEADERS; do test "_$ac_file" = _: && continue
+     case "$ac_file" in
+        *.h) _INP=$ac_file ;;
+        *)
+     esac
+     test ".$_INP" != "." && break
+   done
+fi
+if test ".$_INP" = "."; then
+   case "$_OUT" in
+      */*) _INP=`basename "$_OUT"`
+      ;;
+      *-*) _INP=`echo "$_OUT" | sed -e "s/@<:@_symbol@:>@*-//"`
+      ;;
+      *) _INP=config.h
+      ;;
+   esac
+fi
+if test -z "$_PKG" ; then
+   AC_MSG_ERROR([no prefix for _PREFIX_PKG_CONFIG_H])
+else
+  if test ! -f "$_INP" ; then if test -f "$srcdir/$_INP" ; then
+     _INP="$srcdir/$_INP"
+  fi fi
+  AC_MSG_NOTICE(creating $_OUT - prefix $_UPP for $_INP defines)
+  if test -f $_INP ; then
+    AS_ECHO(["s/^@%:@undef  *\\(@<:@m4_cr_LETTERS[]_@:>@\\)/@%:@undef $_UPP""_\\1/"]) > _script
+    AS_ECHO(["s/^@%:@undef  *\\(@<:@m4_cr_letters@:>@\\)/@%:@undef $_LOW""_\\1/"]) >> _script
+    AS_ECHO(["s/^@%:@def[]ine  *\\(@<:@m4_cr_LETTERS[]_@:>@@<:@_symbol@:>@*\\)\\(.*\\)/@%:@ifndef $_UPP""_\\1\\"]) >> _script
+    AS_ECHO(["@%:@def[]ine $_UPP""_\\1\\2\\"]) >> _script
+    AS_ECHO(["@%:@endif/"]) >> _script
+    AS_ECHO(["s/^@%:@def[]ine  *\\(@<:@m4_cr_letters@:>@@<:@_symbol@:>@*\\)\\(.*\\)/@%:@ifndef $_LOW""_\\1\\"]) >> _script
+    AS_ECHO(["@%:@define $_LOW""_\\1\\2\\"]) >> _script
+    AS_ECHO(["@%:@endif/"]) >> _script
+    # now executing _script on _DEF input to create _OUT output file
+    echo "@%:@ifndef $_DEF"      >$tmp/pconfig.h
+    echo "@%:@def[]ine $_DEF 1" >>$tmp/pconfig.h
+    echo ' ' >>$tmp/pconfig.h
+    echo /'*' $_OUT. Generated automatically at end of configure. '*'/ >>$tmp/pconfig.h
+
+    sed -f _script $_INP >>$tmp/pconfig.h
+    echo ' ' >>$tmp/pconfig.h
+    echo '/* once:' $_DEF '*/' >>$tmp/pconfig.h
+    echo "@%:@endif" >>$tmp/pconfig.h
+    if cmp -s $_OUT $tmp/pconfig.h 2>/dev/null; then
+      AC_MSG_NOTICE([$_OUT is unchanged])
+    else
+      ac_dir=`AS_DIRNAME(["$_OUT"])`
+      AS_MKDIR_P(["$ac_dir"])
+      rm -f "$_OUT"
+      mv $tmp/pconfig.h "$_OUT"
+    fi
+  else
+    AC_MSG_ERROR([input file $_INP does not exist - skip generating $_OUT])
+  fi
+  rm -f conftest.*
+fi
+m4_popdef([_symbol])dnl
+m4_popdef([_script])dnl
+AS_VAR_POPDEF([_INP])dnl
+AS_VAR_POPDEF([_UPP])dnl
+AS_VAR_POPDEF([_LOW])dnl
+AS_VAR_POPDEF([_PKG])dnl
+AS_VAR_POPDEF([_DEF])dnl
+AS_VAR_POPDEF([_OUT])dnl
+],[PACKAGE="$PACKAGE"])])

m4/ax_type_socklen_t.m4

+# ===========================================================================
+#     http://www.gnu.org/software/autoconf-archive/ax_type_socklen_t.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_TYPE_SOCKLEN_T
+#
+# DESCRIPTION
+#
+#   Check whether sys/socket.h defines type socklen_t. Please note that some
+#   systems require sys/types.h to be included before sys/socket.h can be
+#   compiled.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Lars Brinkhoff <lars@nocrew.org>
+#
+#   This program is free software; you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation; either version 2 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 5
+
+AU_ALIAS([TYPE_SOCKLEN_T], [AX_TYPE_SOCKLEN_T])
+AC_DEFUN([AX_TYPE_SOCKLEN_T],
+[AC_CACHE_CHECK([for socklen_t], ac_cv_ax_type_socklen_t,
+[
+  AC_TRY_COMPILE(
+  [#include <sys/types.h>
+   #include <sys/socket.h>],
+  [socklen_t len = 42; return 0;],
+  ac_cv_ax_type_socklen_t=yes,
+  ac_cv_ax_type_socklen_t=no)
+])
+  if test $ac_cv_ax_type_socklen_t != yes; then
+    AC_DEFINE(socklen_t, int, [Substitute for socklen_t])
+  fi
+])

m4/libgcrypt.m4

+dnl Autoconf macros for libgcrypt
+dnl       Copyright (C) 2002, 2004 Free Software Foundation, Inc.
+dnl
+dnl This file is free software; as a special exception the author gives
+dnl unlimited permission to copy and/or distribute it, with or without
+dnl modifications, as long as this notice is preserved.
+dnl
+dnl This file is distributed in the hope that it will be useful, but
+dnl WITHOUT ANY WARRANTY, to the extent permitted by law; without even the
+dnl implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+
+
+dnl AM_PATH_LIBGCRYPT([MINIMUM-VERSION,
+dnl                   [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND ]]])
+dnl Test for libgcrypt and define LIBGCRYPT_CFLAGS and LIBGCRYPT_LIBS.
+dnl MINIMUN-VERSION is a string with the version number optionalliy prefixed
+dnl with the API version to also check the API compatibility. Example:
+dnl a MINIMUN-VERSION of 1:1.2.5 won't pass the test unless the installed
+dnl version of libgcrypt is at least 1.2.5 *and* the API number is 1.  Using
+dnl this features allows to prevent build against newer versions of libgcrypt
+dnl with a changed API.
+dnl
+AC_DEFUN([AM_PATH_LIBGCRYPT],
+[ AC_ARG_WITH(libgcrypt-prefix,
+            AC_HELP_STRING([--with-libgcrypt-prefix=PFX],
+                           [prefix where LIBGCRYPT is installed (optional)]),
+     libgcrypt_config_prefix="$withval", libgcrypt_config_prefix="")
+  if test x$libgcrypt_config_prefix != x ; then
+     if test x${LIBGCRYPT_CONFIG+set} != xset ; then
+        LIBGCRYPT_CONFIG=$libgcrypt_config_prefix/bin/libgcrypt-config
+     fi
+  fi
+
+  AC_PATH_TOOL(LIBGCRYPT_CONFIG, libgcrypt-config, no)
+  tmp=ifelse([$1], ,1:1.2.0,$1)
+  if echo "$tmp" | grep ':' >/dev/null 2>/dev/null ; then
+     req_libgcrypt_api=`echo "$tmp"     | sed 's/\(.*\):\(.*\)/\1/'`
+     min_libgcrypt_version=`echo "$tmp" | sed 's/\(.*\):\(.*\)/\2/'`
+  else
+     req_libgcrypt_api=0
+     min_libgcrypt_version="$tmp"
+  fi
+
+  AC_MSG_CHECKING(for LIBGCRYPT - version >= $min_libgcrypt_version)
+  ok=no
+  if test "$LIBGCRYPT_CONFIG" != "no" ; then
+    req_major=`echo $min_libgcrypt_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\)/\1/'`
+    req_minor=`echo $min_libgcrypt_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\)/\2/'`
+    req_micro=`echo $min_libgcrypt_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\)/\3/'`
+    libgcrypt_config_version=`$LIBGCRYPT_CONFIG --version`
+    major=`echo $libgcrypt_config_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\).*/\1/'`
+    minor=`echo $libgcrypt_config_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\).*/\2/'`
+    micro=`echo $libgcrypt_config_version | \
+               sed 's/\([[0-9]]*\)\.\([[0-9]]*\)\.\([[0-9]]*\).*/\3/'`
+    if test "$major" -gt "$req_major"; then
+        ok=yes
+    else
+        if test "$major" -eq "$req_major"; then
+            if test "$minor" -gt "$req_minor"; then
+               ok=yes
+            else
+               if test "$minor" -eq "$req_minor"; then
+                   if test "$micro" -ge "$req_micro"; then
+                     ok=yes
+                   fi
+               fi
+            fi
+        fi
+    fi
+  fi
+  if test $ok = yes; then
+    AC_MSG_RESULT([yes ($libgcrypt_config_version)])
+  else
+    AC_MSG_RESULT(no)
+  fi
+  if test $ok = yes; then
+     # If we have a recent libgcrypt, we should also check that the
+     # API is compatible
+     if test "$req_libgcrypt_api" -gt 0 ; then
+        tmp=`$LIBGCRYPT_CONFIG --api-version 2>/dev/null || echo 0`
+        if test "$tmp" -gt 0 ; then
+           AC_MSG_CHECKING([LIBGCRYPT API version])
+           if test "$req_libgcrypt_api" -eq "$tmp" ; then
+             AC_MSG_RESULT([okay])
+           else
+             ok=no
+             AC_MSG_RESULT([does not match. want=$req_libgcrypt_api got=$tmp])
+           fi
+        fi
+     fi
+  fi
+  if test $ok = yes; then
+    LIBGCRYPT_CFLAGS=`$LIBGCRYPT_CONFIG --cflags`
+    LIBGCRYPT_LIBS=`$LIBGCRYPT_CONFIG --libs`
+    ifelse([$2], , :, [$2])
+    if test x"$host" != x ; then
+      libgcrypt_config_host=`$LIBGCRYPT_CONFIG --host 2>/dev/null || echo none`
+      if test x"$libgcrypt_config_host" != xnone ; then
+        if test x"$libgcrypt_config_host" != x"$host" ; then
+  AC_MSG_WARN([[
+***
+*** The config script $LIBGCRYPT_CONFIG was
+*** built for $libgcrypt_config_host and thus may not match the
+*** used host $host.
+*** You may want to use the configure option --with-libgcrypt-prefix
+*** to specify a matching config script.
+***]])
+        fi
+      fi
+    fi
+  else
+    LIBGCRYPT_CFLAGS=""
+    LIBGCRYPT_LIBS=""
+    ifelse([$3], , :, [$3])
+  fi
+  AC_SUBST(LIBGCRYPT_CFLAGS)
+  AC_SUBST(LIBGCRYPT_LIBS)
+])