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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

No problem!

It looks like this example is salvageable, nothing is stopping us from just applying the same rules when deducing a template template parameter against other kinds of templates.

This shouldn't stop you from cleaning up the code, whatever rules we come up here are for salvaging old code, not necessarily to entomb these as examples of good practice.

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