[clang] [Clang] Reapply CWG2369 "Ordering between constraints and substitution" (PR #122423)

[via cfe-commits]

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@@ -13458,6 +13473,10 @@ class Sema final : public SemaBase {
   // FIXME: Should we have a similar limit for other forms of synthesis?
   unsigned NonInstantiationEntries;
 
+  /// The number of \p CodeSynthesisContexts that are not constraint
+  /// substitution.
+  unsigned NonConstraintSubstitutionEntries;
+
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cor3ntin wrote:

Why not use a bool flag that is inherited on construction?

https://github.com/llvm/llvm-project/pull/122423