build: configure: have --with-runstatedir overrule --runstatedir

and log that there was runstatedir defined already

configure.ac

@@ -343,7 +343,13 @@ expand_path_option oldincludedir
 expand_path_option infodir
 expand_path_option mandir
 
-AS_IF([test x"${runstatedir}" = x""], [runstatedir="${sbd_runstatedir}"])
+AS_IF([test x"${runstatedir}" = x""], [runstatedir="${sbd_runstatedir}"],
+      [test x"${sbd_runstatedir}" != x""], [
+      echo "--with-runstatedir=${sbd_runstatedir} is taking precedence"
+      echo "over runstatedir=${runstatedir}."
+      echo "Consider using --runstatedir=${sbd_runstatedir} directly or let it"
+      echo "go with the default."
+      runstatedir="${sbd_runstatedir}"])
 expand_path_option runstatedir "${localstatedir}/run"
 AC_SUBST(runstatedir)