Re-vendor, primarily for https://github.com/containers/storage/pull/11

containers/storage got new dependencies, so we will need to re-vendor
eventually anyway, and having this separate from other major work is
cleaner.

But the primary goal of this commit is to see whether it makes skopeo
buildable on OS X.

vendor/golang.org/x/sys/unix/syscall.go

@@ -0,0 +1,69 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+// Package unix contains an interface to the low-level operating system
+// primitives.  OS details vary depending on the underlying system, and
+// by default, godoc will display OS-specific documentation for the current
+// system.  If you want godoc to display OS documentation for another
+// system, set $GOOS and $GOARCH to the desired system.  For example, if
+// you want to view documentation for freebsd/arm on linux/amd64, set $GOOS
+// to freebsd and $GOARCH to arm.
+// The primary use of this package is inside other packages that provide a more
+// portable interface to the system, such as "os", "time" and "net".  Use
+// those packages rather than this one if you can.
+// For details of the functions and data types in this package consult
+// the manuals for the appropriate operating system.
+// These calls return err == nil to indicate success; otherwise
+// err represents an operating system error describing the failure and
+// holds a value of type syscall.Errno.
+package unix // import "golang.org/x/sys/unix"
+
+// ByteSliceFromString returns a NUL-terminated slice of bytes
+// containing the text of s. If s contains a NUL byte at any
+// location, it returns (nil, EINVAL).
+func ByteSliceFromString(s string) ([]byte, error) {
+	for i := 0; i < len(s); i++ {
+		if s[i] == 0 {
+			return nil, EINVAL
+		}
+	}
+	a := make([]byte, len(s)+1)
+	copy(a, s)
+	return a, nil
+}
+
+// BytePtrFromString returns a pointer to a NUL-terminated array of
+// bytes containing the text of s. If s contains a NUL byte at any
+// location, it returns (nil, EINVAL).
+func BytePtrFromString(s string) (*byte, error) {
+	a, err := ByteSliceFromString(s)
+	if err != nil {
+		return nil, err
+	}
+	return &a[0], nil
+}
+
+// Single-word zero for use when we need a valid pointer to 0 bytes.
+// See mkunix.pl.
+var _zero uintptr
+
+func (ts *Timespec) Unix() (sec int64, nsec int64) {
+	return int64(ts.Sec), int64(ts.Nsec)
+}
+
+func (tv *Timeval) Unix() (sec int64, nsec int64) {
+	return int64(tv.Sec), int64(tv.Usec) * 1000
+}
+
+func (ts *Timespec) Nano() int64 {
+	return int64(ts.Sec)*1e9 + int64(ts.Nsec)
+}
+
+func (tv *Timeval) Nano() int64 {
+	return int64(tv.Sec)*1e9 + int64(tv.Usec)*1000
+}
+
+func TimevalToNsec(tv Timeval) int64 { return int64(tv.Sec)*1e9 + int64(tv.Usec)*1e3 }