[clang] [Clang] Avoid assertion failure for initialized extern aliases (PR #223124)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

@keepyixiao btw, please do not rebase once you've pushed a PR up for review (https://llvm.org/docs/GitHub.html#rebasing-pull-requests-and-force-pushes), that makes it much harder for reviewers to check out old comments and the history of the PR as it's changed over time.

https://github.com/llvm/llvm-project/pull/223124