po: fix update-po target to take account of libvirt.pot in srcdir

Now that we're storing libvirt.pot in git, it will be in srcdir instead
of builddir. Weblate is responsible for running msgmerge when the .pot
file changes, so add a warning that this target is not for general usage.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

po/Makefile.am

@@ -43,13 +43,16 @@ SED_PO_FIXUP_ARGS = \
 
 update-gmo: $(GMOFILES)
 
+# The results of this target should not be committed to Git. The Weblate
+# service is responsible for updating .po files when the .pot is changed.
 update-po: $(POTFILE)
+	cd $(srcdir) && \
 	for lang in $(LANGS); do \
 	  echo "Minimizing $$lang content" && \
 	  $(MSGMERGE) --no-location --no-fuzzy-matching --sort-output \
 	    $$lang.po $(POTFILE) | \
-	  $(SED) $(SED_PO_FIXUP_ARGS) > $(srcdir)/$$lang.po-t && \
-	  mv $$lang.po-t $$lang.po
+	  $(SED) $(SED_PO_FIXUP_ARGS) > $$lang.po-t && \
+	  mv $$lang.po-t $$lang.po ; \
 	done
 
 $(POTFILE): POTFILES