Dissallow non-empty metadata for invariant.group

Summary:
This feature is not needed, but it might be usefull in the future
to use metadata to mark what which function should support it
(and strip it when not).

Reviewers: rsmith, sanjoy, amharc, kuhar

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D45419

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332787 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed