mod_status: Report total CPU time accurately when using a threaded

MPM.

Note: It worked before with linuxthreads and it still does.  But now
it works with normal thread implementations too.

PR:     23795


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@101614 13f79535-47bb-0310-9956-ffa450edef68