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

[Tarun Prabhu via llvm-commits]

tarunprabhu wrote:

@nikic 

Could you take a look again and see if your concerns have been addressed.

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