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

[Aaron Ballman via cfe-commits]

AaronBallman 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: [#88265 (comment)](https://github.com/llvm/llvm-project/pull/88265#discussion_r1571088366)

THAT is why this was so familiar to me! :-D Thanks!

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