Cygwin: signal: implement signalfd

First cut of a signalfd implementation.

Still TODO: Non-polling select.

This should mostly work as on Linux except for missing support
for some members of struct signalfd_siginfo, namely ssi_fd,
ssi_band (both SIGIO/SIGPOLL, not fully implemented) and ssi_trapno
(HW exception, required HW support).

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/include/sys/signalfd.h

@@ -0,0 +1,54 @@
+/* sys/signalfd.h: define signalfd(2) and struct signalfd_siginfo
+
+This file is part of Cygwin.
+
+This software is a copyrighted work licensed under the terms of the
+Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+details. */
+
+#ifndef	_SYS_SIGNALFD_H
+#define	_SYS_SIGNALFD_H
+
+#include <stdint.h>
+#include <sys/_default_fcntl.h>
+
+enum
+{
+  SFD_CLOEXEC = O_CLOEXEC,
+  SFD_NONBLOCK = O_NONBLOCK
+};
+#define SFD_CLOEXEC SFD_CLOEXEC
+#define SFD_NONBLOCK SFD_NONBLOCK
+
+struct signalfd_siginfo
+{
+  uint32_t	ssi_signo;
+  int32_t	ssi_errno;
+  int32_t	ssi_code;
+  uint32_t	ssi_pid;
+  uint32_t	ssi_uid;
+  int32_t	ssi_fd;
+  uint32_t	ssi_tid;
+  uint32_t	ssi_band;
+  uint32_t	ssi_overrun;
+  uint32_t	ssi_trapno;
+  int32_t	ssi_status;
+  int32_t	ssi_int;
+  uint64_t	ssi_ptr;
+  uint64_t	ssi_utime;
+  uint64_t	ssi_stime;
+  uint64_t	ssi_addr;
+  uint8_t	pad[48];
+};
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int signalfd (int, const sigset_t *, int);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _SYS_SIGNALFD_H */