[clang] [Clang] Allow raw string literals in C as an extension (PR #88265)

[via cfe-commits]

Sirraide wrote:

> I think we should allow users to enable them in C++03 modes if -fraw-string-literals is passed. I think it's fine to have -fno-raw-string-literals that allows users to disable them in C++03 mode (in case an earlier command line option opted into them and the user wants to disable the feature for some reason), but I don't know if that's worth the effort to support because I don't think we should allow -fno-raw-string-literals in C++11 mode.

In that case I think it might just make sense to ignore the flag in C++11 and later then and allow it before C++11.

> Btw, it seems that precommit CI found some valid issues to be addressed

Ah, I didn’t know that all new warnings should have a `-W` flag associated with them; it seems I’ve somehow only ever added errors so far. I’ll take a look at what happened there.

https://github.com/llvm/llvm-project/pull/88265