[clang] [llvm] [llvm] Add triples for managarm (PR #87845)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> @MaskRay seems like this target might be too niche to go into LLVM at this time? is it worth considering some bar before accepting such a thing into LLVM, rather than encouraging folks to maintain such a thing in a branch for now?

Good question about the acceptance bar. I started https://discourse.llvm.org/t/new-clang-toolchain-acceptance-criteria/79233 

https://github.com/llvm/llvm-project/pull/87845