[clang] [C23] Implement WG14 N3037 (PR #132939)

[Aaron Ballman via cfe-commits]

================
@@ -43,6 +43,9 @@ struct StructuralEquivalenceContext {
   /// key: (from, to, IgnoreTemplateParmDepth)
   using NonEquivalentDeclSet = llvm::DenseSet<std::tuple<Decl *, Decl *, int>>;
 
+  /// The language options to use for making a structural equivalence check.
+  const LangOptions &LangOpts;
+
----------------
AaronBallman wrote:

Good question! I originally did that, but the problem there is: those AST contexts can be different *and can have different language options set*. So I made it explicit and force the caller to set the language options.

https://github.com/llvm/llvm-project/pull/132939