Propagate __attribute__((returns_twice)) from C to IL.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@141002 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/AttributeList.cpp b/lib/Sema/AttributeList.cpp
index 9d366ad..13a0ede 100644
--- a/lib/Sema/AttributeList.cpp
+++ b/lib/Sema/AttributeList.cpp
@@ -159,7 +159,7 @@
     .Case("address_space", AT_address_space)
     .Case("opencl_image_access", AT_opencl_image_access)
     .Case("always_inline", AT_always_inline)
-    .Case("returns_twice", IgnoredAttribute)
+    .Case("returns_twice", AT_returns_twice)
     .Case("vec_type_hint", IgnoredAttribute)
     .Case("objc_exception", AT_objc_exception)
     .Case("objc_method_family", AT_objc_method_family)