936f6a1c3c
executed the make job with sigprocmask(SIG_BLOCK) in effect for a number of signals including SIGCHLD. This caused recursive submakes of the make process in question not to receive SIGCHLDs when their jobs exited. This was a second, independent cause of bin/18895 in addition to the race condition already fixed. Fixed by unblocking all signals before executing the job.