Due to a now default-enabled `undef` pass (llvm/llvm-project
1b1c8d83d3567a60280291c0adb95d1d60335509), a whole bunch of interop
IRGen tests are failing due to missing `undefs`, even though they don't
matter in these tests at all. Add regex matches so that these tests just
check for the name and types of the functions they care about.