Restore trigger freshness check

This reverts commit db19323db2.
Paths are adjusted. The condition is inverted to actually check the
right thing.

The test is moved before build to make it easier to see. Meson does
the .in substitutions immediately after configuration, so this should
be easier to see.

systemd.spec

@@ -467,6 +467,14 @@ CONFIGURE_OPTS=(
 %endif
 
 %meson "${CONFIGURE_OPTS[@]}"
+
+new_triggers=%{_vpath_builddir}/src/rpm/triggers.systemd.sh
+if ! diff -u %{SOURCE1} ${new_triggers}; then
+   echo -e "\n\n\nWARNING: triggers.systemd in Source1 is different!"
+   echo -e "      cp $PWD/${new_triggers} %{SOURCE1}\n\n\n"
+   sleep 5
+fi
+
 %meson_build
 
 %install