[llvm] LCA: migrate from DA to LAA; fix cost computation (PR #107691)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

[Actual results](http://llvm-compile-time-tracker.com/compare.php?from=ec3e5c9e73d2d356ffa09a5f9075eba7e09040a8&to=28daa444b957bdf97707a489e3eb6b4c111ce264&stat=instructions:u).

https://github.com/llvm/llvm-project/pull/107691