clean up DSO builds on OS/390 a bit by ignoring some generated files

and by passing libtool the OS/390-specific options needed to split
the main httpd executable into a small executable with main() and a
dll with everything else (previously this information was hard-coded
in the OS/390 libtool program)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89124 13f79535-47bb-0310-9956-ffa450edef68