Adds check for pending signals in the special ibl xfer trampoline. If there are pending signals, we transfer control to the unlinked ibl entry point instead.
This is required to ensure that we exit the fcache and bound delivery time for signals received while executing fragments that use the special ibl xfer mechanism.
This new check is currently on the fast path, but is verified to not affect performance. Future work to use a cleaner strategy that doesn't affect fast path is i#4804.
Increases sleep time to 1s in drwrap-test-detach to allow more time for pre and post instrumentation to be invoked. pre and post count seem to be zero with the current sleep duration of 1ms.
Fixes: #4670 (closed)