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

[Sam McCall via cfe-commits]

sam-mccall wrote:

Here's a preprocessed file: [repro.zip](https://github.com/llvm/llvm-project/files/15250584/repro.zip)

I tried to reduce, and got rid of most of the test code and some of the stdexec code, but there's still a lot left.
I hit the end of my timebox on that. Maybe creduce can do better.

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