Get mod_file_cache to refuse to compile on systems with neither

sendfile nor mmap.

Get mod_file_cache to compile on systems with sendfile but !mmap.

Submitted by:	Greg Stein


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88623 13f79535-47bb-0310-9956-ffa450edef68