Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -31,6 +31,13 @@
 #define _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
 #endif
 
+#if defined(_LIBCPP_ABI_UNSTABLE)
+// The only purpose of the always_inline thing is ABI stability.
+// Disable it when building for unstable ABI.
+#define _LIBCPP_INLINE_VISIBILITY
+#define _LIBCPP_ALWAYS_INLINE
+#endif
+
 #define _LIBCPP_CONCAT1(_LIBCPP_X,_LIBCPP_Y) _LIBCPP_X##_LIBCPP_Y
 #define _LIBCPP_CONCAT(_LIBCPP_X,_LIBCPP_Y) _LIBCPP_CONCAT1(_LIBCPP_X,_LIBCPP_Y)