Get SINGLE_LISTEN_UNSERIALIZED_ACCEPT working again. This defines that

macro on those platforms that have it defined in 1.3.  The only platform
that doesn't work yet is Linux 2.2.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86933 13f79535-47bb-0310-9956-ffa450edef68