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

[via cfe-commits]

Sirraide wrote:

> Why gnu99 mode and not gnu89 mode? I see GCC has that behavior, but I'm not certain why.

We went over this a while back: https://github.com/llvm/llvm-project/pull/88265#discussion_r1571088366

> I'm not certain there's any harm in always supporting raw string literals from dependency scanning, so we could probably do that in the worst case.

But my concerns from https://github.com/llvm/llvm-project/pull/93753#issuecomment-2173666602 are still relevant too. CC @jansvoboda11

:+1:

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