[llvm] Add SuperH (1-4a) target (PR #181287)

[via llvm-commits]

LunaTheFoxgirl wrote:

I've read it, as denoted by this PR being a draft, it is not ready to merge yet. This work is mainly motivated by the Dreamcast homebrew community and I expect more people will join in to maintain this as I get more progress done, I will notify maintainers here once it's ready to be properly reviewed.

https://github.com/llvm/llvm-project/pull/181287