Refactor pkg/archive with a platform-independent stat struct

pkg/archive contains code both invoked from cli (cross platform) and
daemon (linux only) and Unix-specific dependencies break compilation on
Windows. We extracted those stat-related funcs into platform specific
implementations at pkg/system and added unit tests.

Signed-off-by: Ahmet Alp Balkan <ahmetb@microsoft.com>

archive/archive_unix.go

@@ -0,0 +1,39 @@
+// +build !windows
+
+package archive
+
+import (
+	"errors"
+	"syscall"
+
+	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
+)
+
+func setHeaderForSpecialDevice(hdr *tar.Header, ta *tarAppender, name string, stat interface{}) (nlink uint32, inode uint64, err error) {
+	s, ok := stat.(*syscall.Stat_t)
+
+	if !ok {
+		err = errors.New("cannot convert stat value to syscall.Stat_t")
+		return
+	}
+
+	nlink = uint32(s.Nlink)
+	inode = uint64(s.Ino)
+
+	// Currently go does not fil in the major/minors
+	if s.Mode&syscall.S_IFBLK == syscall.S_IFBLK ||
+		s.Mode&syscall.S_IFCHR == syscall.S_IFCHR {
+		hdr.Devmajor = int64(major(uint64(s.Rdev)))
+		hdr.Devminor = int64(minor(uint64(s.Rdev)))
+	}
+
+	return
+}
+
+func major(device uint64) uint64 {
+	return (device >> 8) & 0xfff
+}
+
+func minor(device uint64) uint64 {
+	return (device & 0xff) | ((device >> 12) & 0xfff00)
+}