utils: fix compilation on Darwin

Although Docker daemon does not work on Darwin, the API client will have
to work. That said, I'm fixing the compilation of the package on Darwin.
Upstream-commit: 2b55874584f034b5113359ced6b05c143d31e03c
Component: engine

components/engine/utils/uname_darwin.go

@@ -2,9 +2,12 @@ package utils
 
 import (
 	"errors"
-	"syscall"
 )
 
-func uname() (*syscall.Utsname, error) {
+type Utsname struct {
+	Release [65]byte
+}
+
+func uname() (*Utsname, error) {
 	return nil, errors.New("Kernel version detection is not available on darwin")
 }

components/engine/utils/uname_linux.go

@@ -4,8 +4,9 @@ import (
 	"syscall"
 )
 
-// FIXME: Move this to utils package
-func uname() (*syscall.Utsname, error) {
+type Utsname syscall.Utsname
+
+func uname() (*Utsname, error) {
 	uts := &syscall.Utsname{}
 
 	if err := syscall.Uname(uts); err != nil {