[llvm-branch-commits] [clang] [llvm] [Clang][Lex] Fix __has_include_next to return false when no valid next dir (PR #173717)

[Zachary Fogg via llvm-branch-commits]

zfogg wrote:

Created #173721 targeting `main` with the same fix. This PR (#173717) is the backport to `release/21.x`.

https://github.com/llvm/llvm-project/pull/173717