[llvm] [CodeGen] Derive the regalloc pipeline from the allocator, remove -optimize-regalloc (PR #215740)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Disabled auto-merge given code formatting is failing. Can we get that fixed before merging (it doesn't block automerge).

https://github.com/llvm/llvm-project/pull/215740