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

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

No impact on compile time: see [results from LLVM Compile Time Tracker](http://llvm-compile-time-tracker.com/compare.php?from=725fab987d7b2133293eb4b82e8a0e9c6ba76053&to=7e3fe5ea9322799c94a4f0bfb842e9b967b57e2d&stat=instructions:u).

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