Modified __GNUC__ vsnprintf prototype declaration to exclude OSX

bstrlib.c

@@ -2755,7 +2755,7 @@
 #define START_VSNBUFF (256)
 #else
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !defined(__APPLE__)
 /* Something is making gcc complain about this prototype not being here, so 
    I've just gone ahead and put it in. */
 extern int vsnprintf (char *buf, size_t count, const char *format, va_list arg);