[llvm] [StackColoring] Change the StackColoring logic + enables it to handle spills (PR #143800)

[via llvm-commits]

Ralender wrote:

After a bit of heuristics tuning, I got rid of the regression in average on code-size
here are the new results:
```
exec-time: 0%
compile-time: 0%
code-size: -0.1%
prologepilog.NumBytesStackSpace: -1.4% and no regressions
```

https://github.com/llvm/llvm-project/pull/143800