[clang][Interp] Fix refers_to_enclosing_variable_or_capture DREs

They do not count into lambda captures, so visit them lazily.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -3894,6 +3894,13 @@ bool ByteCodeExprGen<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
     if (IsPtr)
       return this->emitGetThisFieldPtr(Offset, E);
     return this->emitGetPtrThisField(Offset, E);
+  } else if (const auto *DRE = dyn_cast<DeclRefExpr>(E);
+             DRE && DRE->refersToEnclosingVariableOrCapture() &&
+             isa<VarDecl>(D)) {
+    if (!this->visitVarDecl(cast<VarDecl>(D)))
+      return false;
+    // Retry.
+    return this->visitDeclRef(D, E);
   }
 
   // Try to lazily visit (or emit dummy pointers for) declarations

clang/test/AST/Interp/lambda.cpp

@@ -264,3 +264,6 @@ namespace CaptureDefaults {
   };
   static_assert(f2() == 3, "");
 }
+
+constexpr auto t4 = ([x=42]() consteval { return x; }());
+static_assert(t4 == 42, "");