This is similar to CL 136816 for x/sys/unix, changing the FreeBSD ABI to use 64-bit inodes in
Stat_t, Statfs_t, and Dirent types.

The changes are forward compatible, that is FreeBSD 10.x, 11.x continue to use their current sysnum numbers.
The affected types are converted to the new layout (with some overhead).
Thus the same statically linked binary should work using the native sysnums (without any conversion) on FreeBSD 12.

Breaking API changes in package syscall are:
Mknod takes a uint64 (C dev_t) instead of int.
Stat_t: Dev, Ino, Nlink, Rdev, Gen became uint64.
  Atimespec, Mtimespec, Ctimespec, Birthtimespec renamed to Atim, Mtim, Ctim, Birthtim respectively.

Statfs_t: Mntonname and Mntfromname changed from [88]int8 to [1024]int8 arrays.

Dirent: Fileno became uint64, Namlen uint16 and an additional field Off int64 (currently unused) was added.

The following commands were run to generate ztypes_* and zsyscall_* on FreeBSD-12.0-ALPHA6 systems (GOARCH=386 were run on the same amd64 host):
GOOS=freebsd GOARCH=amd64 ./mksyscall.pl -tags freebsd,amd64 syscall_bsd.go syscall_freebsd.go syscall_freebsd_amd64.go |gofmt >zsyscall_freebsd_amd64.go
GOOS=freebsd GOARCH=amd64 go tool cgo -godefs types_freebsd.go | GOOS=freebsd GOARCH=amd64 go run mkpost.go >ztypes_freebsd_amd64.go

GOOS=freebsd GOARCH=386 ./mksyscall.pl -l32 -tags freebsd,386 syscall_bsd.go syscall_freebsd.go syscall_freebsd_386.go |gofmt >zsyscall_freebsd_386.go
GOOS=freebsd GOARCH=386 go tool cgo -godefs types_freebsd.go | GOOS=freebsd GOARCH=386 go run mkpost.go >ztypes_freebsd_386.go

GOOS=freebsd GOARCH=arm ./mksyscall.pl -l32 -arm -tags freebsd,arm syscall_bsd.go syscall_freebsd.go syscall_freebsd_arm.go |gofmt >zsyscall_freebsd_arm.go
GOOS=freebsd GOARCH=arm go tool cgo -godefs -- -fsigned-char types_freebsd.go | GOOS=freebsd GOARCH=arm go run mkpost.go >ztypes_freebsd_arm.go

The Kevent struct was changed to use the FREEBSD_COMPAT11 version always (requiring the COMPAT_FREEBSD11 kernel option FreeBSD-12, this is the default).

The definitions of ifData were not updated, their functionality in has have been replaced by vendored golang.org/x/net/route.

freebsdVersion initialization was dropped from init() in favor of a sync.Once based wrapper - supportsABI().

Updates #22448.

Change-Id: I359b756e2849c036d7ed7f75dbd6ec836e0b90b4
Reviewed-on: https://go-review.googlesource.com/c/138595
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Background:
The 64-bit inode project was merged into the upcoming FreeBSD 12 release.
It changes the ABI for structs holding inodes: stat, statfs, dirent.
New system call numbers were introduced which accept the new struct layouts,
the old ones were marked as COMPAT11.
Their equivalent libc wrappers are using ELF symbol versioning.
The new wrappers have moved from @FBSD_1.0 to @FBSD_1.5.

Backward and forward compatability is achieved by always using the new struct
layouts while converting the old struct instance to the new layout on old kernels.
https://svnweb.freebsd.org/base?view=revision&revision=318736
https://svnweb.freebsd.org/base?view=revision&revision=320278

The same approach is used for Go:
The new Stat_t, Statfs_t and Dirent types hold 64-bit inodes and additional ABI
changes, they are generated from their C definitions in FreeBSD-12 using cgo -godefs.
Each type has an unexported *_freebsd11 counterpart generated the same way.
Previous directly exposed syscalls like Fstat have now a wrapper in place calling
either fstat or fstat_freebsd12 zsyscall wrapper based on the kern.osreldate.
If an old syscall needs to be used, then the returned *_freebsd11 result is converted
to the new layout before returning from the wrapper.

Introduce supportsABI() call to check the kern.osreldate sysctl for the ABI version.
Drop the old struct stat8 definition in favour of the <sys/stat.h> version.
Run the mktypes part of GOOS=freebsd GOARCH={386,amd64,arm} ./mkall.sh
on FreeBSD-12.0-ALPHA6 (r338675), updating all types except Kevent.

Expose Mknodat, both COMPAT11 version (currently missing) and the FreeBSD 12 one.
Some COMPAT11 syscalls have no direct FreeBSD 12 counterpart, in those cases
an *at(AT_FDCWD, ...) is used instead.

Updates golang/go#22448

Change-Id: I87940b88ae358db88103cdcd06f9cafbf4694cfc
Reviewed-on: https://go-review.googlesource.com/c/136816
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Giovanni Bajo <rasky@develer.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

…n Stat_t on FreeBSD

CL 138595 introduced the new names when the hardcoded stat8 definitions was replaced
with a cgo generated one.

Fixes #29393
Updates #22448

Change-Id: I6309958306329ff301c17344b2e0ead0cc874224
Reviewed-on: https://go-review.googlesource.com/c/155958
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes golang#22447
Fixes golang#22448

Change-Id: Ia24f42c31e014c79040ff927f1247dfb2318de4f
Reviewed-on: https://go-review.googlesource.com/c/160778
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

Fixes golang#22447
Fixes golang#22448

Change-Id: Ia24f42c31e014c79040ff927f1247dfb2318de4f
Reviewed-on: https://go-review.googlesource.com/c/160778
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>