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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

macOS precommit CI failure is unrelated (Flang has their own preprocessor that's separate from Clang's), but the Windows one seems to be related because it's checking output of line directives.

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