Should end up somewhere in the signal handler, typically at the first instruction.
Watch for kernel bugs, can instead let the process exit.
There are now a couple of tests that handle signal delivery while stepping and
the TaskState machinery has been expanded to handle it (see
LinuxPtraceTaskState.Running.handleTrapEvent()). Kernel bugs have been found,
sigh (see bug #3997). A test could be added to make sure that we land on the
first instruction of the signal handler.