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

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

I am awaiting C++20 build bots to be updated to 17.0.6.

FYI: @cor3ntin @AaronBallman with this change, clang 17.0.6 would be the minimum version to build LLVM in C++20 after this change.
Would you like me to announce it somewhere or update some docs to reflect this ?

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