Throughout, change USE_CYGSERVER to USE_SERVER.

* Makefile.in (LIBSERVER): Define and use.
* configure.in: Set LIBSERVER as appropriate.
* environ.cc: Rename allow_daemon to allow_server.  Only recognize when
USE_SERVER is defined.

winsup/cygwin/tty.cc

@@ -407,13 +407,13 @@ tty::common_init (fhandler_pty_master *ptym)
    */
   if (wincap.has_security ())
     {
-#ifdef USE_CYGSERVER
+#ifdef USE_SERVER
       if (cygserver_running == CYGSERVER_UNKNOWN)
 	cygserver_init ();
 #endif
 
       if (
-#ifdef USE_CYGSERVER
+#ifdef USE_SERVER
 	  cygserver_running != CYGSERVER_OK &&
 #endif
 	  !SetKernelObjectSecurity (hMainProc,