Add "(const void *)" back to the hack variable assignments to avoid

Add "(const void *)" back to the hack variable assignments to avoid
warnings like this on Tru64 (and perhaps other platforms):

cc: Warning: exports.c, line 349: In the initializer for
ap_hack_apr_dbm_nextkey, the referenced type of the pointer value
"apr_dbm_nextkey" is "function (pointer to struct apr_dbm_t, pointer
to struct declared without a tag) returning int", which is not
compatible with "const void". (ptrmismatch)
const void *ap_hack_apr_dbm_nextkey = apr_dbm_nextkey;
--------------------------------------^

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87301 13f79535-47bb-0310-9956-ffa450edef68