Please backport d8352e93c1c8042d9166eab3d76d6c07ef585b6d

[ADKaster]

I'm trying to use swift-shipped clang from swfitly use 6.0-snapshot to build https://github.com/ladybirdbrowser/ladybird , and I'm running into llvm#53815

This issue was fixed for 18.x by llvm@d8352e9 in upstream PR llvm#83103

[DougGregor]

Merged the fix to the 6.0 release branch, thank you!