[llvm] ConstraintElim: add dry-run routine to fail early (PR #99670)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> I can check that this is NFC from a code-gen perspective for SPEC and some other larger workloads in the next few days. Please ping me if you don't hear from me by Thursday :)

Ping :)

https://github.com/llvm/llvm-project/pull/99670