[clang] [Webkit Checkers][SaferCpp] Fix MemoryUnsafeCastChecker to precisely exclude `*this` casts (PR #210180)

[Ryosuke Niwa via cfe-commits]

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@@ -254,6 +254,9 @@ class CanMakeWeakPtrBase {
   void initializeWeakPtrFactory() const {
     auto &this_to_T = static_cast<const WeakPtrFactoryType&>(*this);
   }
+  void initializeWeakPtrFactoryReinterpret() const {
+    auto &this_to_T = reinterpret_cast<const WeakPtrFactoryType&>(*this);
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rniwa wrote:

Hm... I think we want to only permit this type of cast when the type we're casting to is a CRTP parameter, not whenever we're casting `this` or `*this`.

https://github.com/llvm/llvm-project/pull/210180