unix: use setattrlist for UtimesNanoAt on Darwin

Use to setarrlist to implement UtimesNanoAt with nanosecond precision
(on Mac OS 10.13 with APFS). Translate AT_SYMLINK_NOFOLLOW to
FSOPT_NOFOLLOW correspondingly.

Change-Id: I1468a1f4eecb53b2280ff6329b1ec64e204701f1
Reviewed-on: https://go-review.googlesource.com/75650
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/mkerrors.sh

@@ -426,6 +426,7 @@ ccflags="$@"
 		$2 ~ /^UTIME_/ ||
 		$2 ~ /^XATTR_(CREATE|REPLACE)/ ||
 		$2 ~ /^ATTR_(BIT_MAP_COUNT|(CMN|VOL|FILE)_)/ ||
+		$2 ~ /^FSOPT_/ ||
 		$2 ~ /^WDIOC_/ ||
 		$2 !~ "WMESGLEN" &&
 		$2 ~ /^W[A-Z0-9]+$/ ||