go-fuzz hangs when the testee forks a subprocess then crashes

[yasushi-saito]

The problem is that the three control FDs (3, 4, 5) used by the testee to communicate with the tester aren't marked close-on-exec. So if the testee forks and dies, the child will keep the tester from completing the reads of the descriptors. Adding

	for _, fd := range []uintptr{3, 4, 5} {
		r1, r2, err := syscall.Syscall(syscall.SYS_FCNTL, fd, syscall.F_GETFD, 0)
		_, _, err = syscall.Syscall(syscall.SYS_FCNTL, fd, syscall.F_SETFD, r1|syscall.FD_CLOEXEC)
	}

at the beginning of Fuzz function fixes this problem. This logic should really be added somewhere go-fuzz-dep/main.go.