Fix a problem in the new --enable-layout functionality where

it wouldn't allow overrides from variables like --prefix,
--bindir, etc.

Obtained from:  Partly from an autoconf-generated configure script.
Submitted by:	Thom May <thom@planetarytramp.net>
Reviewed by:	Aaron Bannert, Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93738 13f79535-47bb-0310-9956-ffa450edef68