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

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Sirraide wrote:

> I think making it so that the test passes (actually handles raw string literals) and updating the FIXME in DependencyDirectivesScanner.cpp should be fine

To clarify, that means setting the `RawStringLiterals` LangOpt in `DependencyDirectivesScanner.cpp`, right? I’m assuming yes, but I just want to make sure.

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