[clang] [clang] Implement CWG2428 "Deprecating a concept" (PR #92295)

[Shafik Yaghmour via cfe-commits]

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@@ -167,9 +167,11 @@ Parser::DeclGroupPtrTy Parser::ParseTemplateDeclarationOrSpecialization(
                                   LastParamListWasEmpty);
 
   // Parse the actual template declaration.
-  if (Tok.is(tok::kw_concept))
-    return Actions.ConvertDeclToDeclGroup(
-        ParseConceptDefinition(TemplateInfo, DeclEnd));
+  if (Tok.is(tok::kw_concept)) {
+    Decl *ConceptDecl = ParseConceptDefinition(TemplateInfo, DeclEnd);
+    ParsingTemplateParams.complete(ConceptDecl);
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shafik wrote:

Curious, why do we need this?

https://github.com/llvm/llvm-project/pull/92295