[clang] [Clang][Sema] Fix a crash in lambda instantiation (PR #85565)

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@@ -13714,6 +13714,12 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
 
     // Capturing 'this' is trivial.
     if (C->capturesThis()) {
+      // We need ThisType here.
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Sirraide wrote:

This comment doesn’t really explain anything. I’d suggest explaining *why*, not *that*, we need a `ThisScope` here.

https://github.com/llvm/llvm-project/pull/85565