Merge r1825169 from trunk:

Propose backportable fix to accept libxml2 path in the
base form or the absolute path to include tree form.

Nowhere does the --with-libxml2= arg suggest the path
is that of the include tree, and disagrees with httpd's
use of --with- syntax for package location.



Submitted by: wrowe
Reviewed by: wrowe, ylavic, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1825720 13f79535-47bb-0310-9956-ffa450edef68