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

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eaeltsin wrote:

@mizvekov - can you please take a look at https://godbolt.org/z/ahro3vnPd ?

This is what I ended up reducing yet another `xtensor` thing that failed with too deep recursive template instantiation with relaxed argument matching and compiled okay without relaxed argument matching.

The reduced example fails somewhat differently, but it complains on `implicit instantiation of undefined template` _with_ relaxed argument matching enabled and compiles OK without...


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