Suppress unavoidable -Wformat-literal in wx[F]printf()

Disable gcc format string checks inside these functions.

include/wx/wxcrtvararg.h

@@ -276,6 +276,8 @@
 #endif
 
 
+wxGCC_ONLY_WARNING_SUPPRESS(format-nonliteral)
+
 WX_DEFINE_VARARG_FUNC_SANS_N0(int, wxPrintf, 1, (const wxFormatString&),
                               wxCRT_PrintfNative, wxCRT_PrintfA)
 inline int wxPrintf(const wxFormatString& s)
@@ -290,6 +292,8 @@ inline int wxFprintf(FILE *f, const wxFormatString& s)
     return wxFprintf(f, wxASCII_STR("%s"), s.InputAsString());
 }
 
+wxGCC_ONLY_WARNING_RESTORE(format-nonliteral)
+
 // va_list versions of printf functions simply forward to the respective
 // CRT function; note that they assume that va_list was created using
 // wxArgNormalizer<T>!