Unconditionally use the WSA equivalents of Socket error constants.

This change will only apply to mingw compilers, and has been found
necessary by late versions of the mingw-w64 compiler. It's the same as
what is done elsewhere for the Microsoft compilers.

If this doesn't upset older compilers in the buildfarm, it will be
backpatched to 9.1.

Problem reported by Michael Cronenworth, although not his patch.

src/include/port/win32.h

@@ -272,36 +272,26 @@ typedef int pid_t;
 #undef EINTR
 #define EINTR WSAEINTR
 #define EAGAIN WSAEWOULDBLOCK
-#ifndef EMSGSIZE
+#undef EMSGSIZE
 #define EMSGSIZE WSAEMSGSIZE
-#endif
-#ifndef EAFNOSUPPORT
+#undef EAFNOSUPPORT
 #define EAFNOSUPPORT WSAEAFNOSUPPORT
-#endif
-#ifndef EWOULDBLOCK
+#undef EWOULDBLOCK
 #define EWOULDBLOCK WSAEWOULDBLOCK
-#endif
-#ifndef ECONNRESET
+#undef ECONNRESET
 #define ECONNRESET WSAECONNRESET
-#endif
-#ifndef EINPROGRESS
+#undef EINPROGRESS
 #define EINPROGRESS WSAEINPROGRESS
-#endif
-#ifndef ENOBUFS
+#undef ENOBUFS
 #define ENOBUFS WSAENOBUFS
-#endif
-#ifndef EPROTONOSUPPORT
+#undef EPROTONOSUPPORT
 #define EPROTONOSUPPORT WSAEPROTONOSUPPORT
-#endif
-#ifndef ECONNREFUSED
+#undef ECONNREFUSED
 #define ECONNREFUSED WSAECONNREFUSED
-#endif
-#ifndef EBADFD
+#undef EBADFD
 #define EBADFD WSAENOTSOCK
-#endif
-#ifndef EOPNOTSUPP
+#undef EOPNOTSUPP
 #define EOPNOTSUPP WSAEOPNOTSUPP
-#endif
 
 /*
  * For Microsoft Visual Studio 2010 and above we intentionally redefine