config magic for enabling DAV, Expat, and SDBM.

*) AP_LIBS contains the target .a files from src/lib/
*) AP_LIB_DIRS contains add'l directories (besides pcre and apr) that we
   will build (and generate Makefiles for)
*) apache_need_expat and apache_need_sdbm are two new configure feature
   macros; set by the DAV stuff as needed
*) hackery to deal with dav/fs/ since it isn't really a module
*) do endian testing, so we can feed it into Expat to optimize that code


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85743 13f79535-47bb-0310-9956-ffa450edef68