Break out more header info into separate files. Use appropriate header files

throughout.
* shared.h: Remove.
* cygwin_version.h: New file.
* delqueue.h: New file.
* environ.h: New file.
* host_dependent.h: New file.
* perprocess.h: New file.
* registry.h: New file.
* security.h: New file.

winsup/cygwin/poll.cc

@@ -9,6 +9,7 @@
    details. */
 
 #include "winsup.h"
+#include <sys/time.h>
 #include <sys/poll.h>
 #include <errno.h>
 #include "fhandler.h"