Merge branch 'jk/push-client-deadlock-fix' into HEAD

Some Windows SDK lacks pthread_sigmask() implementation and fails to compile the recently updated "git push" codepath that uses it. * jk/push-client-deadlock-fix: Windows: only add a no-op pthread_sigmask() when needed Windows: add pthread_sigmask() that does nothing t5504: drop sigpipe=ok from push tests fetch-pack: isolate sigpipe in demuxer thread send-pack: isolate sigpipe in demuxer thread run-command: teach async threads to ignore SIGPIPE send-pack: close demux pipe before finishing async process