Fix apxs -g handling.

Move config_vars.mk from the top build directory to the build directory.
Get build/rules.mk cleaned up for distclean/extraclean.

PR:     10163
        (This is the 2nd of two commits for that PR.  The first was to
        apxs.in -- rev 1.35.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93923 13f79535-47bb-0310-9956-ffa450edef68