xxx: isnanf() is some wtf

gtk/fallback-c89.c

@@ -93,15 +93,27 @@ isnan (double x)
 #endif
 
 #ifndef HAVE_DECL_ISNANF
+#if 1
+#define isnanf(x) isnan(x)
+#else
 /* it seems of the supported compilers only
  * MSVC does not have isnanf(), but it does
  * have _isnanf() which does the same as isnanf()
  */
+#ifdef _MSC_VER
 static inline gboolean
 isnanf (float x)
 {
   return _isnanf (x);
 }
+#elif defined (__GNUC__)
+/* gcc has an intern function that it warns about when
+ * using -Wshadow but no header properly declares it,
+ * so we do it instead.
+ */
+extern int isnanf (float x);
+#endif
+#endif
 #endif
 
 #ifndef INFINITY