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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> Thanks, guarding the second specialization with the feature test macro works.
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> I will try to reduce the test case tomorrow, if you still need this.
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> 

Thanks. If it's not too much work for you, that would be great. Otherwise, I think a pretty good guess can be made from reading the source code, but I may not be able to try until next week. If that happens and I still don't manage to reproduce it, I will ask again.

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