[InstCombine] add tests to show potential missing folds; NFC

As noted in https://bugs.llvm.org/show_bug.cgi?id=33138 and
the comments, there are multiple ways to view this. If we
choose not to solve this in InstCombine, these tests will
serve as documentation of that choice.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303755 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed