finish getting apxs to work with a binary build

it now picks up any necessary ld environment variables from
the envvars file when invoking "httpd -l" to verify that
mod_so was included in the build


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94865 13f79535-47bb-0310-9956-ffa450edef68