In svnserve, ensure that all use of the shared pool data type is wrapped
in #if APR_HAS_THREADS.

* subversion/svnserve/svnserve.c
  (serve_thread_t): Define the shared_pool member within #if APR_HAS_THREADS.
   There is no need to declare the shared_pool as a 'struct' after typedef.
  (main): No need to declare the shared_pool as a 'struct' after typedef.

Found by: brane


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1527286 13f79535-47bb-0310-9956-ffa450edef68