[llvm] [ADT] Allow reverse to find free rbegin/rend functions (PR #87840)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

My version of clang format (16) thinks the code is already formatted, and in addition is consistent with the other adl functions above, so I'm going to leave this as-is without appeasing the formatting bot.

https://github.com/llvm/llvm-project/pull/87840