Fix a cmake compatiblity issue related to quoting with cmake 2.8.12
and later.

PR: 56615
Submitted by: Chuck Liu <cliu81 gmail.com>, trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1625196 13f79535-47bb-0310-9956-ffa450edef68