Merge r1618541 from trunk:

Avoid useless warning message when parsing a section guarded by <IfDefine foo> if $(foo) is used within the section.
PR 56503

Submitted by: jailletc36
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1621603 13f79535-47bb-0310-9956-ffa450edef68