[clang] [flang] [llvm] Introduce -fexperimental-loop-fuse to clang and flang (PR #142686)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I'm fine with this as well.

For the future though, I think we can save a lot of time by exposing experimental passes via `-mllvm -enable-loop-fusion`. That is still easy for users to experiment with, while being less intrusive.

https://github.com/llvm/llvm-project/pull/142686