[llvm] [SSAUpdaterBulk] Add PHI simplification pass. (PR #132004)

[Valery Pykhtin via llvm-commits]

vpykhtin wrote:

Hi @nikic, sorry for the mess, I've replaced this PR with new stacked version, https://github.com/llvm/llvm-project/pull/135180, I had to start it someday.

https://github.com/llvm/llvm-project/pull/132004