utils: Support __has_feature() macro on non-LLVM compilers by returning 0

src/libstrongswan/utils/utils.h

@@ -112,6 +112,13 @@ void utils_deinit();
 #define BUILD_ASSERT_ARRAY(a) \
 		BUILD_ASSERT(!__builtin_types_compatible_p(typeof(a), typeof(&(a)[0])))
 
+/**
+ * LLVM/Clang __has_feature support
+ */
+#ifndef __has_feature
+# define __has_feature(x) 0
+#endif
+
 /**
  * Debug macro to follow control flow
  */