[clang] [clang-tools-extra] [Clang] Treat line directives as header names. (PR #211512)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! It should also come with a release note (and documentation in the language extensions docs?).

I think we should likely have an extension diagnostic for accepting a header-name, specifically the `<>` form (which shouldn't be disruptive given that no existing code uses that form). I don't think it's worth the effort for the `""` form given the expected disruptions, but maybe you feel differently.

https://github.com/llvm/llvm-project/pull/211512