[x86] consolidate and add tests for undef binop folds; NFC

As was already shown in the div/rem tests and noted in PR36305,
the behavior is inconsistent, but it's not limited to div/rem only.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324678 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed