* configure.in: Substitute MOD_SO_ENABLED variable.

* support/apxs.in: Use it to eliminate run-time check for whether
httpd has mod_so built-in.

Submitted by: David M. Lee <dmlee crossroads.com>
PR: 40653


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@494781 13f79535-47bb-0310-9956-ffa450edef68