[llvm] [LoopUnroll] Add flag to disable profile usage (PR #102950)

[Ellis Hoag via llvm-commits]

ellishg wrote:

Thanks @nikic, using `-fno-unroll-loops` did indeed give us a size win and I think that's the direction we will go in. However, I still see value in this PR. The `-loop-unroll-use-branch-weights=false` flag would have been hugely helpful for me to triage the size regression I saw when consuming profiles. This also allows users to consume profiles without changing the behavior of this pass.

In fact, I believe that **all** optimizations passes that use profile data should have the option to disable profile data usage. Many passes already have flags like this (although the flag names are widely inconsistent and difficult to find). I also added a similar flag in https://github.com/llvm/llvm-project/pull/102956.

https://github.com/llvm/llvm-project/pull/102950