For some reason AC_PREFIX_DEFAULT must not be called before the apr

m4 files are included. This fixes builds on autoconf 2.52 again.

Obtained from:  Sander Striker
Submitted by:	Thom May <thom@planetarytramp.net>
Reviewed by:	Aaron Bannert


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93639 13f79535-47bb-0310-9956-ffa450edef68