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/arc_summary/.gitignore

@@ -1 +0,0 @@
-arc_summary

cmd/arc_summary/Makefile.am

@@ -1,8 +1,8 @@
-bin_SCRIPTS = arc_summary
+bin_SCRIPTS += arc_summary
+CLEANFILES  += arc_summary
 
-CLEANFILES = arc_summary
-EXTRA_DIST = arc_summary3
-SCRIPT = arc_summary3
+EXTRA_DIST += %D%/arc_summary3
+ARC_SUMMARY = %D%/arc_summary3
 
-arc_summary: $(SCRIPT)
-	cp $< $@
+arc_summary: $(ARC_SUMMARY)
+	$(AM_V_at)cp $< $@