Configure to get along with 2.9 clang

llvm-svn: 136526
diff --git a/libcxx/src/exception.cpp b/libcxx/src/exception.cpp
index b0efda6..28d87b3 100644
--- a/libcxx/src/exception.cpp
+++ b/libcxx/src/exception.cpp
@@ -56,6 +56,7 @@
     return __sync_fetch_and_add(&__terminate_handler, (std::terminate_handler)0);
 }
 
+_ATTRIBUTE(noreturn)
 void
 std::terminate() _NOEXCEPT
 {