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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I am awaiting C++20 build bots to be updated to 17.0.6. (cc: @ilya-biryukov)
> 
> 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 ?

It should be announced in the release notes as well as the Announcements channel so people are aware. That said, I am still concerned with bumping the minimum version up that much. Clang 5.0 (Sep 2017) to Clang 17.0 (Nov 2023) is quite the jump. This might not be a bad thing to float via an RFC in Discourse before announcing it as our final decision just to make sure we get community buy-in. I don't think it will be contentious (there's not much to be done; when we want to switch to C++20 for the code base, we're going to need to make a significant leap anyway), but best to make sure this won't be disruptive to anyone in ways that we can address.

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