When using pthread_kill, the signal should be delivered to the
specified thread. Current implementation, however, may add the
signal to the groups pending list, if the signal is masked at the
time of dispatch. From the group's pending list it can be delivered
to any thread of the group, which is wrong.
Fix this by adding a new field "FAR struct tcb_s *tcb" to
"struct sigpendq", marking if the signal needs to be delivered
to a specific thread. Use NULL for the value if delivery to any
thread in the group is ok.
Signed-off-by: Jukka Laitinen <jukka.laitinen@tii.ae>