* server/mpm/event/event.c,

* server/mpm/event/event.c,
  server/mpm/simple/simple_run.c,
  support/htcacheclean.c: Adjust use of APR_RING macros to
  ensure the APR_RING_HEAD is always embedded in a containing
  structure, to avoid warnings with GCC 11.  (apr_ring.h also
  suggests this is best practice)

See also: https://bugzilla.redhat.com/show_bug.cgi?id=1957353
          https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98503
          msgid <814cca2a-1992-3fae-bb0e-c84b3d09b73b@gmail.com>
Github: closes #186

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1889957 13f79535-47bb-0310-9956-ffa450edef68