diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -496,6 +496,10 @@
 #define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
 #endif
 
+#if __has_builtin(__builtin_constant_p)
+#define _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
+#endif
+
 #if !__is_identifier(__has_unique_object_representations)
 #define _LIBCPP_HAS_UNIQUE_OBJECT_REPRESENTATIONS
 #endif
@@ -537,9 +541,7 @@
 
 #if _GNUC_VER >= 700
 #define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
-#endif
-
-#if _GNUC_VER >= 700
+#define _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
 #define _LIBCPP_HAS_UNIQUE_OBJECT_REPRESENTATIONS
 #endif
 
@@ -1533,6 +1535,12 @@
 #  define _LIBCPP_FOPEN_CLOEXEC_MODE
 #endif
 
+#ifdef _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
+#define _LIBCPP_BUILTIN_CONSTANT_P(x) __builtin_constant_p(x)
+#else
+#define _LIBCPP_BUILTIN_CONSTANT_P(x) false
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG