[llvm] [GlobalISel] Combine [s,z]ext of undef into 0 (PR #117439)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

I am never going to touch `propagate_undef_any_op`. Go ahead.

It took a lot of energy and time to get the anyext(undef) in shape. It didn't want to loose it.

https://github.com/llvm/llvm-project/pull/117439