unix: add MNT_* flags on DragonflyBSD

Change-Id: I0326a7bfcf3cd794eb1158055a8ee98a396d3b47
Reviewed-on: https://go-review.googlesource.com/136818
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

@@ -87,6 +87,7 @@ includes_DragonFly='
 #include <sys/stat.h>
 #include <sys/sysctl.h>
 #include <sys/mman.h>
+#include <sys/mount.h>
 #include <sys/wait.h>
 #include <sys/ioctl.h>
 #include <net/bpf.h>

unix/zerrors_dragonfly_amd64.go

@@ -880,6 +880,40 @@ const (
 	MAP_VPAGETABLE                    = 0x2000
 	MCL_CURRENT                       = 0x1
 	MCL_FUTURE                        = 0x2
+	MNT_ASYNC                         = 0x40
+	MNT_AUTOMOUNTED                   = 0x20
+	MNT_CMDFLAGS                      = 0xf0000
+	MNT_DEFEXPORTED                   = 0x200
+	MNT_DELEXPORT                     = 0x20000
+	MNT_EXKERB                        = 0x800
+	MNT_EXPORTANON                    = 0x400
+	MNT_EXPORTED                      = 0x100
+	MNT_EXPUBLIC                      = 0x20000000
+	MNT_EXRDONLY                      = 0x80
+	MNT_FORCE                         = 0x80000
+	MNT_IGNORE                        = 0x800000
+	MNT_LAZY                          = 0x4
+	MNT_LOCAL                         = 0x1000
+	MNT_NOATIME                       = 0x10000000
+	MNT_NOCLUSTERR                    = 0x40000000
+	MNT_NOCLUSTERW                    = 0x80000000
+	MNT_NODEV                         = 0x10
+	MNT_NOEXEC                        = 0x4
+	MNT_NOSUID                        = 0x8
+	MNT_NOSYMFOLLOW                   = 0x400000
+	MNT_NOWAIT                        = 0x2
+	MNT_QUOTA                         = 0x2000
+	MNT_RDONLY                        = 0x1
+	MNT_RELOAD                        = 0x40000
+	MNT_ROOTFS                        = 0x4000
+	MNT_SOFTDEP                       = 0x200000
+	MNT_SUIDDIR                       = 0x100000
+	MNT_SYNCHRONOUS                   = 0x2
+	MNT_TRIM                          = 0x1000000
+	MNT_UPDATE                        = 0x10000
+	MNT_USER                          = 0x8000
+	MNT_VISFLAGMASK                   = 0xf1f0ffff
+	MNT_WAIT                          = 0x1
 	MSG_CMSG_CLOEXEC                  = 0x1000
 	MSG_CTRUNC                        = 0x20
 	MSG_DONTROUTE                     = 0x4