[clang] [clang] Return larger CXX records in memory (PR #120670)

[Pranav Kant via cfe-commits]

pranavk wrote:

Oops. Too bad. I didn't realize we branched off release/20.x 

Anyhow, I made necessary tweaks to now make it a LLVM 21 feature.

> There is a X86 Support section

It feels more appropriate to put this in "ABI changes section" than "X86 support" since it's not a "support". But I am happy to move that over if that's the precedence for these kind of changes. Let me know. 

https://github.com/llvm/llvm-project/pull/120670