unix: add UTIME_* constants on Linux

They might be used as special values in struct Timespec. See
http://man7.org/linux/man-pages/man2/utimensat.2.html for details.

Change-Id: I1c2d6d7731ca7f077d033e51ee6421a4f2cfbb89
Reviewed-on: https://go-review.googlesource.com/72376
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/zerrors_linux_386.go b/unix/zerrors_linux_386.go
index 4066ad1..245f585 100644
--- a/unix/zerrors_linux_386.go
+++ b/unix/zerrors_linux_386.go
@@ -1842,6 +1842,8 @@
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
 	UMOUNT_NOFOLLOW                      = 0x8
+	UTIME_NOW                            = 0x3fffffff
+	UTIME_OMIT                           = 0x3ffffffe
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb