[llvm] Revert "[STLExtras] Remove incorrect hack to make indexed_accessor_range operator== compatible with C++20" (PR #72265)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Probably the right thing here would've been to commit the revert without sending a pull request.

Specifically, for now, a pull request is a signal that this patch needs review - so committing a sent pull request without approval is an indication of process failure/that code that needed review was committed without review. So, please don't do that (either commit directly if it doesn't need precommit review, or post a pull request and wait for review if it needs precommit review)

https://github.com/llvm/llvm-project/pull/72265