the alias of an InstAlias instead of the thing being aliased. Because we need to
know the features that are valid for an InstAlias.
This is part of a work-in-progress.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127986 91177308-0d34-0410-b5e6-96231b3b80d8