[libcxx-commits] [libcxx] [libc++] Allow the use of extensions in the implementation (PR #79532)

[Sam McCall via libcxx-commits]

sam-mccall wrote:

No worries @EricWF, thanks for your help.

The regression is time spent in ASTReader::ReadPragmaDiagnosticMappings, which explains why it's modules-specific.

![image](https://github.com/llvm/llvm-project/assets/548993/5c007ebc-7bf0-4c73-b210-be57c545c1a3)

here's the baseline

![image](https://github.com/llvm/llvm-project/assets/548993/7ce9cdea-d9c9-493b-bb3c-f3e1ba24ffbe)

and a ridiculously-wide screenshot of just that function

![image](https://github.com/llvm/llvm-project/assets/548993/34a6b411-6096-4981-91a3-6390e75aa11b)

(sorry I don't have a reasonable way to share the underlying data)

https://github.com/llvm/llvm-project/pull/79532