Silence nullability extension warnings with GCC ##build

Author: radare

libr/include/r_types_null.h

@@ -10,8 +10,13 @@ extern "C" {
 // -Wno-nullability-completeness
 
 #ifdef __clang__
+#if __has_warning("-Wnullability-completeness")
 #pragma clang diagnostic ignored "-Wnullability-completeness"
 #endif
+#if __has_warning("-Wnullability-extension")
+#pragma clang diagnostic ignored "-Wnullability-extension"
+#endif
+#endif
 
 #if defined(__clang__)
   // Clang supports _Nonnull / _Nullable with -fnullability