Enable mod_mem_cache to use apr_atomic operators in managing cache_object

reference counting. Enabled by default via the USE_ATOMICS preproc directive.
This compiles cleanly and serves pages on Windows. Not compiled or tested on
any other OS.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93889 13f79535-47bb-0310-9956-ffa450edef68