* cygerrno.h: Make multi-inclusion safe.

* fhandler_termios.cc (fhandler_termios::tcsetpgrp): Deal with EINTR.
* dcrt0.cc (dll_crt0_0): Accommodate init_console_handler argument change.
* winsup.h: Ditto.
* fhandler_tty.cc (fhandler_tty_slave::open): Ditto.
* exceptions.cc (init_console_handler): Ditto.  Ignore console events if we're
not attached to a terminal.
* fhandler_tty.cc (fhandler_tty_slave::open): Ditto.
* wincap.cc: Implement has_null_console_handler_routine throughout.
* wincap.h: Ditto.

winsup/cygwin/cygerrno.h

@@ -8,6 +8,8 @@ This software is a copyrighted work licensed under the terms of the
 Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
+#ifndef _CYGERRNO_H
+#define _CYGERRNO_H
 #include <errno.h>
 
 void __stdcall seterrno_from_win_error (const char *file, int line, DWORD code) __attribute__ ((regparm(3)));
@@ -47,3 +49,4 @@ class save_errno
 
 extern const char *__sp_fn;
 extern int __sp_ln;
+#endif /*_CYGERRNO_H*/