[flang] [llvm] [flang] Add HOSTNM runtime and lowering intrinsics implementation (PR #131910)

[via llvm-commits]

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

Lowering looks good, just a couple style nits!
My request has to do with the lit tests, that should not be end-to-end executable tests.

https://github.com/llvm/llvm-project/pull/131910