[clang] [llvm] Change what counts as printable to match glibc (PR #231223)

[Harald van Dijk via cfe-commits]

hvdijk wrote:

@cor3ntin Updated with the completely different approach now, I think it's ready for review, thanks. The changes to how characters are printed in diagnostics, as seen in the updated tests, I'm not entirely sure that's the best thing to do in all cases, but as long as it doesn't do harm I think it's probably good to just be consistent.

https://github.com/llvm/llvm-project/pull/231223