[clang] Force an ICE when reentrantly reading a concept decl (PR #224677)

[Chuanqi Xu via cfe-commits]

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@@ -3249,7 +3249,14 @@ class ImplicitConceptSpecializationDecl final
     : public Decl,
       private llvm::TrailingObjects<ImplicitConceptSpecializationDecl,
                                     TemplateArgument> {
-  unsigned NumTemplateArgs;
+  unsigned NumTemplateArgs : 31;
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ChuanqiXu9 wrote:

What I had in mind was:

``
#ifndef NDEBUG
...
#else
...
#endif

https://github.com/llvm/llvm-project/pull/224677