Added [[noreturn]] attribute everywhere it should be

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@132125 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/__config b/include/__config
index ef03e62..48f3a44 100644
--- a/include/__config
+++ b/include/__config
@@ -116,8 +116,10 @@
 #define _LIBCPP_HAS_NO_DECLTYPE
 #endif
 
-#if !(__has_feature(cxx_attributes))
-#define _LIBCPP_HAS_NO_ATTRIBUTES
+#if __has_feature(cxx_attributes)
+#  define _ATTRIBUTE(x) [[x]]
+#else
+#  define _ATTRIBUTE(x) __attribute__ ((x))
 #endif
 
 #define _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS