unix: add Fstatat on Solaris

Updates golang/go#24381

Change-Id: I9bd15bb7961f02af12a45b12ac62e07d059c744e
Reviewed-on: https://go-review.googlesource.com/100555
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/syscall_solaris.go

@@ -595,9 +595,10 @@ func Poll(fds []PollFd, timeout int) (n int, err error) {
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error)
 //sys	Fdatasync(fd int) (err error)
-//sys Flock(fd int, how int) (err error)
+//sys	Flock(fd int, how int) (err error)
 //sys	Fpathconf(fd int, name int) (val int, err error)
 //sys	Fstat(fd int, stat *Stat_t) (err error)
+//sys	Fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
 //sys	Fstatvfs(fd int, vfsstat *Statvfs_t) (err error)
 //sys	Getdents(fd int, buf []byte, basep *uintptr) (n int, err error)
 //sysnb	Getgid() (gid int)

unix/zsyscall_solaris_amd64.go

@@ -50,6 +50,7 @@ import (
 //go:cgo_import_dynamic libc_flock flock "libc.so"
 //go:cgo_import_dynamic libc_fpathconf fpathconf "libc.so"
 //go:cgo_import_dynamic libc_fstat fstat "libc.so"
+//go:cgo_import_dynamic libc_fstatat fstatat "libc.so"
 //go:cgo_import_dynamic libc_fstatvfs fstatvfs "libc.so"
 //go:cgo_import_dynamic libc_getdents getdents "libc.so"
 //go:cgo_import_dynamic libc_getgid getgid "libc.so"
@@ -176,6 +177,7 @@ import (
 //go:linkname procFlock libc_flock
 //go:linkname procFpathconf libc_fpathconf
 //go:linkname procFstat libc_fstat
+//go:linkname procFstatat libc_fstatat
 //go:linkname procFstatvfs libc_fstatvfs
 //go:linkname procGetdents libc_getdents
 //go:linkname procGetgid libc_getgid
@@ -303,6 +305,7 @@ var (
 	procFlock,
 	procFpathconf,
 	procFstat,
+	procFstatat,
 	procFstatvfs,
 	procGetdents,
 	procGetgid,
@@ -772,6 +775,19 @@ func Fstat(fd int, stat *Stat_t) (err error) {
 	return
 }
 
+func Fstatat(fd int, path string, stat *Stat_t, flags int) (err error) {
+	var _p0 *byte
+	_p0, err = BytePtrFromString(path)
+	if err != nil {
+		return
+	}
+	_, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&procFstatat)), 4, uintptr(fd), uintptr(unsafe.Pointer(_p0)), uintptr(unsafe.Pointer(stat)), uintptr(flags), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
 func Fstatvfs(fd int, vfsstat *Statvfs_t) (err error) {
 	_, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&procFstatvfs)), 2, uintptr(fd), uintptr(unsafe.Pointer(vfsstat)), 0, 0, 0, 0)
 	if e1 != 0 {