[arcmt] Revert r156999 "Remove the "it is not safe to remove an unused 'autorelease' message" ARC
migration error".

Per feedback from John this is useful to have in general.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157198 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed