Use WIN32 for Windows-specific #ifdef guards

To support Microsoft Visual C++, we must not guard Windows-specific code
in MinGW-specific #ifdef guards.

Happily, even 64-bit MSVC defines the WIN32 constant, therefore we can use
that instead.

[JES: fixed commit message, reordered commit, split out unrelated changes]
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

libvncclient/listen.c

@@ -27,11 +27,13 @@
 #endif
 #include <unistd.h>
 #include <sys/types.h>
-#ifdef __MINGW32__
+#ifdef WIN32
 #define close closesocket
 #include <winsock2.h>
+#ifdef _MINGW32
 #undef max
-#else
+#endif // #ifdef _MINGW32
+#else // #ifdef WIN32
 #include <sys/wait.h>
 #include <sys/utsname.h>
 #endif
@@ -46,7 +48,7 @@
 void
 listenForIncomingConnections(rfbClient* client)
 {
-#ifdef __MINGW32__
+#ifdef WIN32
   /* FIXME */
   rfbClientErr("listenForIncomingConnections on MinGW32 NOT IMPLEMENTED\n");
   return;

libvncclient/sockets.c

@@ -38,7 +38,9 @@
 #ifdef WIN32
 #undef SOCKET
 #include <winsock2.h>
+#ifdef MINGW32
 #define EWOULDBLOCK WSAEWOULDBLOCK
+#endif
 #define close closesocket
 #define read(sock,buf,len) recv(sock,buf,len,0)
 #define write(sock,buf,len) send(sock,buf,len,0)
@@ -109,7 +111,7 @@ ReadFromRFBServer(rfbClient* client, char *out, unsigned int n)
 	  diff.tv_sec--;
 	  diff.tv_usec+=1000000;
         }
-#ifndef __MINGW32__
+#ifndef WIN32
         sleep (diff.tv_sec);
         usleep (diff.tv_usec);
 #else

libvncclient/vncviewer.c

@@ -45,7 +45,7 @@ static rfbBool DummyPoint(rfbClient* client, int x, int y) {
 static void DummyRect(rfbClient* client, int x, int y, int w, int h) {
 }
 
-#ifdef __MINGW32__
+#ifdef WIN32
 static char* NoPassword(rfbClient* client) {
   return strdup("");
 }
@@ -56,9 +56,9 @@ static char* NoPassword(rfbClient* client) {
 #endif
 
 static char* ReadPassword(rfbClient* client) {
-#ifdef __MINGW32__
+#ifdef WIN32
 	/* FIXME */
-	rfbClientErr("ReadPassword on MinGW32 NOT IMPLEMENTED\n");
+	rfbClientErr("ReadPassword on Windows NOT IMPLEMENTED\n");
 	return NoPassword(client);
 #else
 	int i;