[libcxx-commits] [libcxx] Revert "[libc++] Allow the use of extensions in the implementation (#79532)" (PR #85792)

[A. Jiang via libcxx-commits]

frederick-vs-ja wrote:

When building modules, it shouldn't be needed to suppress warning on C++14/17/20 features, right?

I'd expect that C++23 features is rarely used as extensions (or not yet used), so we might be able to suppress the warnings more locally.

https://github.com/llvm/llvm-project/pull/85792