Since we are using AC_CACHE_CHECK, avoid warning

about non-cached item by adding the required _cv_

Submitted by: jim
Backports: r664701


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@669682 13f79535-47bb-0310-9956-ffa450edef68