fs: avoid using unix.UTIME_OMIT on darwin

Change-Id: I8f05010f64edaf1d41fdfca31ee4ae3079cd0ae3

fs/loopback.go

@@ -403,8 +403,8 @@ func (n *LoopbackNode) Setattr(ctx context.Context, f FileHandle, in *fuse.SetAt
 		atime, aok := in.GetATime()
 
 		if mok || aok {
-			ta := unix.Timespec{Nsec: unix.UTIME_OMIT}
-			tm := unix.Timespec{Nsec: unix.UTIME_OMIT}
+			ta := unix.Timespec{Nsec: unix_UTIME_OMIT}
+			tm := unix.Timespec{Nsec: unix_UTIME_OMIT}
 			var err error
 			if aok {
 				ta, err = unix.TimeToTimespec(atime)

fs/loopback_darwin.go

@@ -12,6 +12,8 @@ import (
 	"time"
 )
 
+const unix_UTIME_OMIT = 0x0
+
 // timeToTimeval - Convert time.Time to syscall.Timeval
 //
 // Note: This does not use syscall.NsecToTimespec because

fs/loopback_freebsd.go

@@ -7,6 +7,8 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+const unix_UTIME_OMIT = unix.UTIME_OMIT
+
 // FreeBSD has added copy_file_range(2) since FreeBSD 12. However,
 // golang.org/x/sys/unix hasn't add corresponding syscall constant or
 // wrap function. Here we define the syscall constant until sys/unix

fs/loopback_linux.go

@@ -13,6 +13,8 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+const unix_UTIME_OMIT = unix.UTIME_OMIT
+
 func doCopyFileRange(fdIn int, offIn int64, fdOut int, offOut int64,
 	len int, flags int) (uint32, syscall.Errno) {
 	count, err := unix.CopyFileRange(fdIn, &offIn, fdOut, &offOut, len, flags)