[clang] [clang] Enable C++17 relaxed template template argument matching by default (PR #89807)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> but not having a convenient reproducer is not a good reason to keep the ToT Clang in a broken state

As someone who worked on a different reduction of Sam's reproducer yesterday, and spent whopping 8 hours of work time to get https://github.com/llvm/llvm-project/issues/91566#issuecomment-2102739179, I disagree with your framing. I don't find it acceptable to claim that you provided an actionable reproducer, when it's 400 lines of dense code that can't be reduced automatically, and have half of the names stripped.

https://github.com/llvm/llvm-project/pull/89807