unix: add bindings for setattrlist() on macOS

The setattrlist() function can be used to mutate the attributes of files through a single call. For example, one can perform a chmod(), chown(), chflags(), [...] all at once.

This change also adds bindings for the UF_* and SF_* flags that are accepted by chflags(). This makes it possible to use setattrlist() to perform the equivalent of lchflags(), for which we currently have no binding.

Change-Id: Ib5a604503a984b95a02b65ad1a437246cd170584
GitHub-Last-Rev: 45dd9d475aa72d628eaa4d06221adba6afd60278
GitHub-Pull-Request: golang/sys#155
Reviewed-on: https://go-review.googlesource.com/c/sys/+/481815
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

unix/syscall_darwin.go

@@ -613,6 +613,7 @@ func SysctlKinfoProcSlice(name string, args ...int) ([]KinfoProc, error) {
 //sys	Rmdir(path string) (err error)
 //sys	Seek(fd int, offset int64, whence int) (newoffset int64, err error) = SYS_LSEEK
 //sys	Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *Timeval) (n int, err error)
+//sys	Setattrlist(path string, attrlist *Attrlist, attrBuf []byte, options int) (err error)
 //sys	Setegid(egid int) (err error)
 //sysnb	Seteuid(euid int) (err error)
 //sysnb	Setgid(gid int) (err error)
@@ -675,7 +676,6 @@ func SysctlKinfoProcSlice(name string, args ...int) ([]KinfoProc, error) {
 // Kqueue_from_portset_np
 // Kqueue_portset
 // Getattrlist
-// Setattrlist
 // Getdirentriesattr
 // Searchfs
 // Delete