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

[Mark de Wever via libcxx-commits]

mordante wrote:

> We've talked about allowing extensions on [discourse](https://discourse.llvm.org/t/rfc-use-language-extensions-from-future-standards-in-libc/71898/5) and in a libc++ monthly meeting and agreed to test it out in the LLVM 18 release. We've done that with the `tuple` constructor overload set (using conditional `explicit`). Since we haven't heard about any breakages, it seems safe to do. 

Since we don't have a LLVM-18 release yet and presumably not a lot of usage except for users HEAD I feel this conclusion is premature. I  really like to wait until after the release and see whether we get breakage before moving forward with this patch.

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