This confers an >10x speedup on t/z-t/cmd builds (12s -> 1.1s),
gets rid of 23 redundant identical automake specs and gitignores,
and groups the binaries with their common headers
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes#13259
