For final target classes of which the source type is a unique non-
virtual base, we know that the dynamic_cast succeeding is equivalent to
the vptr pointing to the target's vtable. So check this if possible
instead of calling the more expensive `__dynamic_cast` runtime method.
This might be extend
As of Xcode 16 beta 2 with the macOS 15 SDK, each re-inclusion of the
stddef.h header causes the NULL macro in C++ to be re-defined to an
integral constant (__null). This makes the workaround in d59a576b8
("Redefine NULL to nullptr") ineffective, as other headers that are
typically included after s
