[InstSimplify] add test to demonstrate undef matching differences; NFC

This is a baseline test for D54631.
Patch by:
@nikic (Nikita Popov)



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347055 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed