[RFC] sigpending rework

[Kalaky <kalaky@gmail.com>]

Hello,

Currently, queued RT signals go into a list of pending signals
for a given task_struct (multiple RT signals can be queued).
When an process dequeues a signal through sigwaitinfo()
we must search the list for the given signal. This search is
always O(n) where n is the number of pending signals,
since we must go through all list members to ensure if
a signal number is still pending.

I'm working on converting the sigpending structure into a vector
of _NSIG sigqueue's for each signal number (which is quite a big
work), this way we can directly access each signal list, delivering
and checking any pending signals in a efficient manner.

Any thoughts ?

TIA,

Kalaky