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

[via cfe-commits]

cor3ntin wrote:

Having a clean reduction to decide whether the code is supposed to compile or not is indeed a good first step.

Clang 18 was not conforming and people might have relied on it.

There is a  -fno-relaxed-template-template-args that can be used as a workaround for now

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