[clang] Fixes and closes #53952. Setting the ASTHasCompilerErrors member variable correctly based on the PP diagnostics. (PR #68127)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

Thank you for the fix, the changes LGTM! The precommit CI failure appears to be unrelated to these changes. I don't think this requires test coverage or a release note.

https://github.com/llvm/llvm-project/pull/68127