Perform an optimized block_given? check without accessing a caller's frame. This logic checks if the target method is our built-in block_given? and uses fast logic in that case. All other calls fall back on normal indy call logic. Note that if the target method is initially not built-in, or becomes a not built-in version later, we permanently fall back on the invocation logic. No further checking is done and the site is optimized as a normal call from there.