unix: add UMOUNT_NOFOLLOW constant

Add the UMOUNT_NOFOLLOW on Linux, available since Linux 2.6.34. See
http://man7.org/linux/man-pages/man2/umount.2.html and
https://github.com/torvalds/linux/commit/db1f05bb85d796

Fixes golang/go#18316

Change-Id: I5c7dafdbb311f287b6cf290aa8a0eaf2940b9834
Reviewed-on: https://go-review.googlesource.com/46771
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/mkerrors.sh

@@ -376,7 +376,7 @@ ccflags="$@"
 		$2 == "IFNAMSIZ" ||
 		$2 ~ /^CTL_(MAXNAME|NET|QUERY)$/ ||
 		$2 ~ /^SYSCTL_VERS/ ||
-		$2 ~ /^(MS|MNT)_/ ||
+		$2 ~ /^(MS|MNT|UMOUNT)_/ ||
 		$2 ~ /^TUN(SET|GET|ATTACH|DETACH)/ ||
 		$2 ~ /^(O|F|E?FD|NAME|S|PTRACE|PT)_/ ||
 		$2 ~ /^LINUX_REBOOT_CMD_/ ||

unix/zerrors_linux_386.go

@@ -1755,6 +1755,7 @@ const (
 	TUNSETVNETBE                         = 0x400454de
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb

unix/zerrors_linux_amd64.go

@@ -1756,6 +1756,7 @@ const (
 	TUNSETVNETBE                         = 0x400454de
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb

unix/zerrors_linux_arm.go

@@ -1760,6 +1760,7 @@ const (
 	TUNSETVNETBE                         = 0x400454de
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb

unix/zerrors_linux_arm64.go

@@ -1745,6 +1745,7 @@ const (
 	TUNSETVNETBE                         = 0x400454de
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb

unix/zerrors_linux_mips.go

@@ -1759,6 +1759,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x10
 	VEOL                                 = 0x11

unix/zerrors_linux_mips64.go

@@ -1759,6 +1759,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x10
 	VEOL                                 = 0x11

unix/zerrors_linux_mips64le.go

@@ -1759,6 +1759,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x10
 	VEOL                                 = 0x11

unix/zerrors_linux_mipsle.go

@@ -1759,6 +1759,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x10
 	VEOL                                 = 0x11

unix/zerrors_linux_ppc64.go

@@ -1817,6 +1817,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0x10
 	VEOF                                 = 0x4
 	VEOL                                 = 0x6

unix/zerrors_linux_ppc64le.go

@@ -1817,6 +1817,7 @@ const (
 	TUNSETVNETBE                         = 0x800454de
 	TUNSETVNETHDRSZ                      = 0x800454d8
 	TUNSETVNETLE                         = 0x800454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0x10
 	VEOF                                 = 0x4
 	VEOL                                 = 0x6

unix/zerrors_linux_s390x.go

@@ -1817,6 +1817,7 @@ const (
 	TUNSETVNETBE                         = 0x400454de
 	TUNSETVNETHDRSZ                      = 0x400454d8
 	TUNSETVNETLE                         = 0x400454dc
+	UMOUNT_NOFOLLOW                      = 0x8
 	VDISCARD                             = 0xd
 	VEOF                                 = 0x4
 	VEOL                                 = 0xb