positional-format-strings: suppress -Wformat-non-iso only for clang

positional-format-strings.c

@@ -1,7 +1,9 @@
 #include <stdio.h>
 
 /* suppress "warning: positional arguments are not supported by ISO C" */
+#ifdef __clang__
 #pragma GCC diagnostic ignored "-Wformat-non-iso"
+#endif
 
 int main(void) {
   printf("%3$3.2f %2$s %1$s\n", "One", "Two", 3.0);