[clang] [Clang] Instantiate constexpr function when they are needed. (PR #173537)

[via cfe-commits]

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@@ -622,6 +625,15 @@ Sema::~Sema() {
   SemaPPCallbackHandler->reset();
 }
 
+void Sema::RegisterSemaProxy() {
+  // Let the AST context relies on Sema for
+  // ast mutations features that require semantic analysis
+  // (lazy instantiation, reflection, etc).
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Sirraide wrote:

```suggestion
  // Let the AST context rely on Sema for
  // AST mutation features that require semantic analysis
  // (lazy instantiation, reflection, etc).
```
nit: typos

https://github.com/llvm/llvm-project/pull/173537