Initial windows runtime work

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

mount_unix.go

@@ -1,4 +1,4 @@
-// +build !windows
+// +build linux
 
 package containerd
 
@@ -12,6 +12,10 @@ func (m *Mount) Mount(target string) error {
 	return syscall.Mount(m.Source, target, m.Type, uintptr(flags), data)
 }
 
+func Unmount(mount string, flags int) error {
+	return syscall.Unmount(mount, flags)
+}
+
 // parseMountOptions takes fstab style mount options and parses them for
 // use with a standard mount() syscall
 func parseMountOptions(options []string) (int, string) {