Autodetect the presence of the <sys/param.h> header; use it if available.

This change results in fewer OS dependencies than the old (hardcoded)
"#if defined() &&..." list

Submitted by:   Ovies Brabson <oviesb@us.ibm.com>
Reviewed by:    Martin Kraemer


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@84242 13f79535-47bb-0310-9956-ffa450edef68