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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> @mizvekov - can you please take a look at https://godbolt.org/z/ahro3vnPd ?
> The reduced example fails somewhat differently, but it complains on `implicit instantiation of undefined template` _with_ relaxed argument matching enabled and compiles OK without...

Thank you, this example does look interesting. I will try to reduce further.

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