MFC r351211:sys.kern.pdeathsig.signal_delivered_ptrace: fix startup.PR: 237657
MFC r351210:sys.kern.pdeathsig.signal_delivered_ptrace: fix debugger detachPR: 237657
MFC r332740:Add PROC_PDEATHSIG_SET to procctl interface.MFC r332825:Rename PROC_PDEATHSIG_SET -> PROC_PDEATHSIG_CTL.MFC r333067:Remove redundant pipe from pdeathsig.c test.