supporting piping a buffer to an external process #639

Job	Run time
build (ubuntu-latest)	3m 4s
build (ubuntu-latest, --disable-curses)	2m 42s
build (ubuntu-latest, --disable-lua)	2m 53s
build (ubuntu-latest, --disable-tre)	3m 0s
build (ubuntu-latest, --disable-selinux)	2m 59s
build (ubuntu-latest, --disable-acl)	2m 45s
build (ubuntu-latest, --disable-help)	2m 45s
build (ubuntu-20.04)	3m 9s
build (ubuntu-20.04, --disable-curses)	3m 14s
build (ubuntu-20.04, --disable-lua)	2m 34s
build (ubuntu-20.04, --disable-tre)	2m 47s
build (ubuntu-20.04, --disable-selinux)	3m 4s
build (ubuntu-20.04, --disable-acl)	3m 20s
build (ubuntu-20.04, --disable-help)	3m 12s
	41m 28s

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