+// portable version check for clang
+#ifndef __CLANG_PREREQ
+# if defined __clang__ && defined __clang_major__ && defined __clang_minor__
+/* nolint */
+# define __CLANG_PREREQ(maj, min) \
+ ((__clang_major__ << 16) + __clang_minor__ >= ((maj) << 16) + (min))
+# else
+/* nolint */
+# define __CLANG_PREREQ(maj, min) 0
+# endif
+#endif
+
+#if defined(__has_builtin)
+#define FOLLY_HAS_BUILTIN(...) __has_builtin(__VA_ARGS__)
+#else
+#define FOLLY_HAS_BUILTIN(...) 0
+#endif
+
+#if defined(__has_feature)
+#define FOLLY_HAS_FEATURE(...) __has_feature(__VA_ARGS__)
+#else
+#define FOLLY_HAS_FEATURE(...) 0
+#endif
+