configure: Add AM_SILENT_RULES

Working with “silent make mode” makes debugging a lot of easier
since warnings wont shadowed by useless compiler noise

configure.ac

@@ -3,6 +3,7 @@ AC_INIT(LibVNCServer, 0.9.8, http://sourceforge.net/projects/libvncserver)
 AM_INIT_AUTOMAKE(LibVNCServer, 0.9.8)
 AM_CONFIG_HEADER(rfbconfig.h)
 AX_PREFIX_CONFIG_H([rfb/rfbconfig.h])
+AM_SILENT_RULES([yes])
 
 # Checks for programs.
 AC_PROG_CC