[clang] [clang] Revert default behavior change of P0522R0 implementation (PR #91811)

[via cfe-commits]

cor3ntin wrote:

@erichkeane The goal is to provide a temporary working default, and a proper fix next fix, so that folks who are impacted by the break (everyone working on stdexec) isn't impacted longer than necessary. So I'll go and merge that and we can discuss a longer-term solution monday

https://github.com/llvm/llvm-project/pull/91811