[llvm] [ValueTracking] Extend LHS/RHS with matching operand to work without constants. (PR #85557)

[via llvm-commits]

goldsteinn wrote:

Minimal (but existing) compile time impact: https://llvm-compile-time-tracker.com/compare.php?from=e77378cc14ec712942452aca155addacbe904c8f&to=4fe7d1d86ee416afa476594b4e5d38f342f76498&stat=instructions%3Au

Alternative if we req at least one of L1/R1 to be constant has lower compile time regression but misses a few of the folds:
https://llvm-compile-time-tracker.com/compare.php?from=e77378cc14ec712942452aca155addacbe904c8f&to=ca42cfefc5d89d915e42a3bfd55d6c1993019a6a&stat=instructions:u

https://github.com/llvm/llvm-project/pull/85557