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

[Utkarsh Saxena via llvm-commits]

usx95 wrote:

Build bot has been updated, and the RFC has no pushback. I will land this now.

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