[clang] [Clang][Sema] Disable checking invalid template id in initializer of primary variable template `std::format_kind` with libstdc++ (PR #139560)

[Erich Keane via cfe-commits]

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@@ -4383,6 +4383,11 @@ Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
     };
 
     if (VarDecl *Var = Template->getTemplatedDecl();
+        // Skipping std::format_kind in libstdc++ is a hack for
+        // GH139067 / https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120190
+        !(Var->getName() == "format_kind" &&
+          Var->getDeclContext()->isStdNamespace() &&
+          PP.isMacroDefined("__GLIBCXX__")) &&
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erichkeane wrote:

It would be great if we could find some sort of way to check the actual VERSION of the hack once they fix this, but it doesn't look like they have a fix in flight.

https://github.com/llvm/llvm-project/pull/139560