[libcxx-commits] [libcxx] [libc++][modules] Uses _LIBCPP_USING_IF_EXISTS. (PR #90409)

[Mark de Wever via libcxx-commits]

mordante wrote:

> > This attribute is used in the headers. Not using this in the modules has led to several issues. Add them to the modules to avoid these errors in other placed.
> 
> If they're not needed without modules, then I suspect this is just papering over the root cause of the breakages. Could you point me towards some concrete examples?

We've discussed this privately.

https://github.com/llvm/llvm-project/pull/90409