install libhttpd.exp

install mod_foo.lib and mod_foo.exp for modules which APIs
that other modules need to link against (e.g., mod_dav, mod_proxy,
etc.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1525308 13f79535-47bb-0310-9956-ffa450edef68