7637 restorecontext(ucontext_t *ucp) leaves all maskable signals blocked in curthread->t_hold
Review Request #2532 - Created April 5, 2020 and submitted
Upstream of Joyent OS-5834
Ran reproducer script from Joyent bug, without the changes, it almost immediately crashes w/ a segfault. Running on a PI with the fix does not crash.