Add a __has_extension check for '#pragma clang attribute' as an external-declaration

This was added in r356075.

llvm-svn: 356600
diff --git a/clang/include/clang/Basic/Features.def b/clang/include/clang/Basic/Features.def
index b171365..c97cbc5 100644
--- a/clang/include/clang/Basic/Features.def
+++ b/clang/include/clang/Basic/Features.def
@@ -247,6 +247,7 @@
 // Miscellaneous language extensions
 EXTENSION(overloadable_unmarked, true)
 EXTENSION(pragma_clang_attribute_namespaces, true)
+EXTENSION(pragma_clang_attribute_external_declaration, true)
 
 #undef EXTENSION
 #undef FEATURE
diff --git a/clang/test/Parser/pragma-attribute-context.cpp b/clang/test/Parser/pragma-attribute-context.cpp
index 3ec5a67..d893f18 100644
--- a/clang/test/Parser/pragma-attribute-context.cpp
+++ b/clang/test/Parser/pragma-attribute-context.cpp
@@ -1,6 +1,10 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9.0.0 -verify -std=c++11 %s
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9.0.0 -xobjective-c++ -verify -std=c++11 %s
 
+#if !__has_extension(pragma_clang_attribute_external_declaration)
+#error
+#endif
+
 #define BEGIN_PRAGMA _Pragma("clang attribute push (__attribute__((availability(macos, introduced=1000))), apply_to=function)")
 #define END_PRAGMA _Pragma("clang attribute pop")