Fix parallel make srpm

When building srpm using make -j, each of the recursive makes invoked to
build srpm-{dkms,kmod,utils} will build the dist target. This is both
unnecessary, and also has a very good chance of breaking when they race
trying to build gitrev.

Fix this by make dist a prerequisite of srpm-{dkms,kmod,utils} instead
of srpm-common, so that it will be done once before invoking the
recursive makes.

Also, gitrev is not really required for make dist, so instead of adding
it to BUILT_SOURCES, just add it as a prerequisite of the all target.

Mark the individual package targets as PHONY.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10564

config/rpm.am

@@ -6,6 +6,12 @@
 # Build targets for RPM packages.
 ###############################################################################
 
+PHONY += srpm srpms srpm-kmod srpm-dkms srpm-utils
+PHONY += rpm rpms rpm-kmod rpm-dkms rpm-utils
+PHONY += srpm-common rpm-common rpm-local
+
+srpm-kmod srpm-dkms srpm-utils: dist
+
 srpm-kmod:
 	$(MAKE) $(AM_MAKEFLAGS) pkg="${PACKAGE}-kmod" \
 		def='${SRPM_DEFINE_COMMON} ${SRPM_DEFINE_KMOD}' srpm-common
@@ -54,7 +60,7 @@ rpm-local:
 	cp $(top_srcdir)/scripts/kmodtool $(rpmbuild)/SOURCES && \
 	cp $(distdir).tar.gz $(rpmbuild)/SOURCES)
 
-srpm-common: dist
+srpm-common:
 	@(dist=`$(RPM) --eval %{?dist}`; \
 	rpmpkg=$(pkg)-$(VERSION)-$(RELEASE)$$dist*src.rpm; \
 	rpmspec=$(pkg).spec; \