[llvm] [PatternMatching] Add generic API for matching constants using custom conditions (PR #85676)

[via llvm-commits]

goldsteinn wrote:

> Please check the compile-time impact of this change.

https://llvm-compile-time-tracker.com/compare.php?from=817f453aa576286aaca0a6b0244e6ab08516b80c&to=05871ee629407932bc6576224dcc2ae99db473fa&stat=instructions:u

Think basically no impact, maybe a slight regression stage2-O0 and slight improvement stage2-O3, but looks to be within err range and a bit scattered.

https://github.com/llvm/llvm-project/pull/85676