[clang] [clang] check deduction consistency when partial ordering function templates (PR #100692)

[Alexander Kornienko via cfe-commits]

alexfh wrote:

Our internal releases have been blocked on this issue, since even a local revert is not an option at the moment due to the number of dependent commits and problems in other parts of LLVM. We would appreciate if we could get a resolution in the next day or two. If there's no clear path forward yet or more delays are expected, should we consider reverting this temporarily and relanding with the necessary adjustments? I must say I appreciate the overall responsiveness and readiness to resolve the issues. I just see that there seem to be objective complexities here which may require a bit more time to figure out.

https://github.com/llvm/llvm-project/pull/100692