Cygwin: /proc/<PID>/status: simplify code generating signal info

Cygwin: /proc/<PID>/status: simplify code generating signal info

The code generating the signal info in _pinfo::siginfo() and in
commune_process() are doing the same thing.  Create a local static
function commune_process_siginfo() to have the code in one place
only.  Remove a useless sigpending() call.

Fixes: 9a3c058f6612 ("Cygwin: /proc/<PID>/status: Fill SigPnd, SigBlk and SigIgn values with life")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>