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

[Sam McCall via cfe-commits]

sam-mccall wrote:

@mizvekov Thank you! With that patch, clang not only doesn't crash on stdexec with `-frelaxed-template-template-args`, but in fact accepts the code.


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