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/external.cc

@@ -16,8 +16,9 @@ details. */
 #include "sigproc.h"
 #include "pinfo.h"
 #include <exceptions.h>
-#include "tty.h"
 #include "shared_info.h"
+#include "cygwin_version.h"
+#include "perprocess.h"
 
 static external_pinfo *
 fillout_pinfo (pid_t pid, int winpid)