Centralize variable substitution

A bunch of places need to edit files to incorporate the configured paths
i.e. bindir, sbindir etc. Move this logic into a common file.

Create arc_summary by copying arc_summary[23] as appropriate at build
time instead of install time.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10559

contrib/dracut/90zfs/Makefile.am

@@ -1,3 +1,5 @@
+include $(top_srcdir)/config/Substfiles.am
+
 pkgdracutdir = $(dracutdir)/modules.d/90zfs
 pkgdracut_SCRIPTS = \
 	export-zfs.sh \
@@ -14,27 +16,4 @@ pkgdracut_DATA = \
 	zfs-snapshot-bootfs.service \
 	zfs-rollback-bootfs.service
 
-EXTRA_DIST = \
-	export-zfs.sh.in \
-	module-setup.sh.in \
-	mount-zfs.sh.in \
-	parse-zfs.sh.in \
-	zfs-generator.sh.in \
-	zfs-load-key.sh.in \
-	zfs-needshutdown.sh.in \
-	zfs-lib.sh.in \
-	zfs-env-bootfs.service.in \
-	zfs-snapshot-bootfs.service.in \
-	zfs-rollback-bootfs.service.in
-
-$(pkgdracut_SCRIPTS) $(pkgdracut_DATA) :%:%.in
-	-$(SED) -e 's,@bindir\@,$(bindir),g' \
-		-e 's,@sbindir\@,$(sbindir),g' \
-		-e 's,@udevdir\@,$(udevdir),g' \
-		-e 's,@udevruledir\@,$(udevruledir),g' \
-		-e 's,@sysconfdir\@,$(sysconfdir),g' \
-		-e 's,@systemdunitdir\@,$(systemdunitdir),g' \
-		-e 's,@mounthelperdir\@,$(mounthelperdir),g' \
-		$< >'$@'
-
-CLEANFILES = $(pkgdracut_SCRIPTS) $(pkgdracut_DATA)
+SUBSTFILES += $(pkgdracut_SCRIPTS) $(pkgdracut_DATA)