Check for <wspiapi.h> and use it if present

Should help bug #603527 if glib is built in an environment that has
<wspiapi.h>.

config.h.win32.in

@@ -607,6 +607,13 @@
 /* Have a working bcopy */
 /* #undef HAVE_WORKING_BCOPY */
 
+/* Define to 1 if you have the <wspiapi.h> header file. */
+#ifndef _MSC_VER
+/* #undef HAVE_WSPIAPI_H */
+#else
+#define HAVE_WSPIAPI_H 1
+#endif
+
 /* Define to 1 if xattr is available */
 /* #undef HAVE_XATTR */