[clang] [clang] Change "bad" to "unsupported" in register type error (PR #111550)

[via cfe-commits]

https://github.com/Sirraide approved this pull request.

LGTM

(I’ve definitely seen ‘bad X’ in other places before, and I’ve personally never really had a problem w/ that sort of wording, but I also can’t deny that ‘unsupported X’ is unquestionably clearer ;Þ)

https://github.com/llvm/llvm-project/pull/111550