[llvm] [GlobalIsel] Combine G_PTR_ADD. (PR #95647)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Unfortunately, I cannot check CTMark. There are more ptradd combines and more opportunities to form legal addressing modes. My only concern is about the order of combines.

https://github.com/llvm/llvm-project/pull/95647