[clang] [flang] [llvm] add -floop-fuse to clang and flang (PR #142686)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

I don't think we should expose clang driver options for passes that are known to have significant issues.

If you want to add a `cl::opt` flag to allow scheduling this in the pipeline and accessible for early testing via `-mllvm`, that would be a different matter.

If we *really* want a clang driver option, then it should be named `-fexperimental-fuse-loops`.

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