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

[Vlad Serebrennikov via cfe-commits]

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@@ -0,0 +1,115 @@
+// RUN: %clang_cc1 %s -fsyntax-only -std=c++23                                     -verify=expected,new
+// RUN: %clang_cc1 %s -fsyntax-only -std=c++23 -fno-relaxed-template-template-args -verify=expected,old
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Endilll wrote:

> Since the core issue is not resolved by WG21, I don't want to claim to be resolving it here with this patch.

It'd be far from the first time we're testing an issue that is still open (https://github.com/llvm/llvm-project/blob/bd53c7cce418fe7f3e171859d4718df15d03dc2b/clang/test/CXX/drs/dr24xx.cpp#L62), but the fact that 2398 filing lacks any possible resolution that we can be testing against, it complicates the matter.

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