Add missing sub-MAKE error check. (All other sub-make calls have it).

This error was found by David Harris <dharris@drh.net> (who fixed it
in a different way; I chose the simpler approach).

Submitted by: David Harris <dharris@drh.net>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83724 13f79535-47bb-0310-9956-ffa450edef68