Effort to reduce the number of exported symbols

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@122057 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/__config b/include/__config
index 4af9bec..2b590cc 100644
--- a/include/__config
+++ b/include/__config
@@ -82,7 +82,7 @@
 
 #define _LIBCPP_CANTTHROW __attribute__ ((__nothrow__))
 
-#define _LIBCPP_ALWAYS_INLINE  __attribute__((__always_inline__))
+#define _LIBCPP_ALWAYS_INLINE  __attribute__ ((__visibility__("hidden"), __always_inline__))
 
 #if defined(__clang__)