Update LLVM for rebase to r212749.

Includes a cherry-pick of:
r212948 - fixes a small issue with atomic calls

Change-Id: Ib97bd980b59f18142a69506400911a6009d9df18
diff --git a/lib/ExecutionEngine/RuntimeDyld/ObjectImageCommon.h b/lib/ExecutionEngine/RuntimeDyld/ObjectImageCommon.h
index 4917b93..c3a2182 100644
--- a/lib/ExecutionEngine/RuntimeDyld/ObjectImageCommon.h
+++ b/lib/ExecutionEngine/RuntimeDyld/ObjectImageCommon.h
@@ -48,7 +48,8 @@
   {
     // FIXME: error checking? createObjectFile returns an ErrorOr<ObjectFile*>
     // and should probably be checked for failure.
-    ObjFile.reset(object::ObjectFile::createObjectFile(Buffer->getMemBuffer()).get());
+    std::unique_ptr<MemoryBuffer> Buf(Buffer->getMemBuffer());
+    ObjFile.reset(object::ObjectFile::createObjectFile(Buf).get());
   }
   ObjectImageCommon(std::unique_ptr<object::ObjectFile> Input)
   : ObjectImage(nullptr), ObjFile(std::move(Input))  {}