vim-patch:8.1.0941: macros for MS-Windows are inconsistent (#20215)

Problem:    Macros for MS-Windows are inconsistent, using "32", "3264 and
            others.
Solution:   Use MSWIN for all MS-Windows builds.  Use FEAT_GUI_MSWIN for the
            GUI build. (Hirohito Higashi, closes vim/vim#3932)
4f97475d32

src/nvim/msgpack_rpc/server.c

@@ -94,7 +94,7 @@ char *server_address_new(const char *name)
 {
   static uint32_t count = 0;
   char fmt[ADDRESS_MAX_SIZE];
-#ifdef WIN32
+#ifdef MSWIN
   int r = snprintf(fmt, sizeof(fmt), "\\\\.\\pipe\\%s.%" PRIu64 ".%" PRIu32,
                    name ? name : "nvim", os_get_pid(), count++);
 #else