allow utimes on mac os, only lutimes isn't supported

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)

system/utimes_darwin.go

@@ -0,0 +1,11 @@
+package system
+
+import "syscall"
+
+func LUtimesNano(path string, ts []syscall.Timespec) error {
+	return ErrNotSupportedPlatform
+}
+
+func UtimesNano(path string, ts []syscall.Timespec) error {
+	return syscall.UtimesNano(path, ts)
+}

system/utimes_linux.go

@@ -24,8 +24,5 @@ func LUtimesNano(path string, ts []syscall.Timespec) error {
 }
 
 func UtimesNano(path string, ts []syscall.Timespec) error {
-	if err := syscall.UtimesNano(path, ts); err != nil {
+	return syscall.UtimesNano(path, ts)
-		return err
-	}
-	return nil
 }

system/utimes_unsupported.go

@@ -1,4 +1,4 @@
-// +build !linux,!freebsd
+// +build !linux,!freebsd,!darwin
 
 package system