Called from a non-local return handler. Tests whether the non-local return was meant to be caught by this frame. If it was not, then it rethrows the exception. If the caller is the correct handler, then this function destroys the exception object and returns..
Create an exception object that will be unwound to the frame containing context, return retval.
Returns YES
if this is an LK catch
handler, NO
if it is a cleanup.
Try to read the expected value and fail loudly if you can't.