[LoopVersioningLICM] Add test coverage for llvm.loop.licm_versioning.disable

In the next change, I am generalizing the function
findStringMetadataForLoop and I want to make sure I don't break this.
Looks like there was no coverage for this so far.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267182 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed