[llvm] [CodeGen][NPM] Support generic regalloc-npm option (PR #135149)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Right now other passes can be run here (will need to add a way to mark a pass as a regalloc pass) If `-passes` is used, this argument will be ignored. 

Ignore is bad. If we're going to have this embedded flag, it needs to be a hard error that you can't mix the flags.



https://github.com/llvm/llvm-project/pull/135149