[clang-tools-extra] [llvm] [clang] [STLExtras] Add out-of-line definition of friend operator== for C++20 (PR #72348)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

Clang 17.0.6 fixed https://github.com/llvm/llvm-project/issues/68901. This issue was not present in GCC or MSVC [godbolt](https://godbolt.org/z/YEhK37Mqj).

I have added release notes. I will also file the RFC and wait for comments.

https://github.com/llvm/llvm-project/pull/72348