[llvm] [RegisterCoalescer] Deferring deletion of instructions in `ErasedInstrs` until the end of an iteration (PR #79820)

[Quentin Dian via llvm-commits]

DianQK wrote:

> Also can you add the test from #71178 and #73519

Hmm, this PR doesn't fix it. This test case isn't stable, and I can't test it with RegisterCoalescer.

https://github.com/llvm/llvm-project/pull/79820