1:1 Userland threading stage 2.20/4:

1:1 Userland threading stage 2.20/4:

Unify access to pending threads with a new function, lwp_sigpend(), which
returns pending signals for the lwp, which includes both lwp-specific
signals and signals pending on the process.  The new function lwp_delsig()
is used to remove a certain signal from the pending set of both process and
lwp.

Rework the places which access the pending signal list to either use those
two functions or, where not possibly, to work on both lwp and proc signal
lists.