autoconf: use include directives instead of recursing down cmd

No installation diff, dist lost
  -zfs-2.1.99/cmd/fsck_zfs/fsck.zfs
which was distributed erroneously, since it's generated

Also clean gitrev on clean

Also add -e 'any possible bashisms' to default checkbashisms flags,
and fully parallelise it and shellcheck, and it works out-of-tree, too

Also align the Release in the dist META file correctly

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13316

cmd/fsck_zfs/.gitignore

@@ -1 +0,0 @@
-/fsck.zfs

cmd/fsck_zfs/Makefile.am

@@ -1,7 +1,5 @@
-include $(top_srcdir)/config/Substfiles.am
-include $(top_srcdir)/config/Shellcheck.am
-
-dist_sbin_SCRIPTS = fsck.zfs
-
-SUBSTFILES += $(dist_sbin_SCRIPTS)
-
+sbin_SCRIPTS      += fsck.zfs
+SHELLCHECKSCRIPTS += fsck.zfs
+CLEANFILES        += fsck.zfs
+EXTRA_DIST        += %D%/fsck.zfs.in
+$(call SUBST,fsck.zfs,%D%/)

cmd/fsck_zfs/fsck.zfs.in

@@ -7,13 +7,13 @@
 # see fsck.zfs(8)
 #
 
-if [ "$#" = "0" ]; then
+if [ $# -eq 0 ]; then
 	echo "Usage: $0 [options] dataset…" >&2
 	exit 16
 fi
 
 ret=0
-for dataset in "$@"; do
+for dataset; do
 	case "$dataset" in
 		-*)
 			continue