vendor: update buildkit to v0.8

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/docker/docker/pkg/system/rm.go

@@ -1,3 +1,5 @@
+// +build !darwin,!windows
+
 package system // import "github.com/docker/docker/pkg/system"
 
 import (

vendor/github.com/docker/docker/pkg/system/rm_windows.go

@@ -0,0 +1,6 @@
+package system
+
+import "os"
+
+// EnsureRemoveAll is an alias to os.RemoveAll on Windows
+var EnsureRemoveAll = os.RemoveAll

vendor/github.com/docker/docker/pkg/system/stat_bsd.go

@@ -1,3 +1,5 @@
+// +build freebsd netbsd
+
 package system // import "github.com/docker/docker/pkg/system"
 
 import "syscall"

vendor/github.com/docker/docker/pkg/system/stat_solaris.go

@@ -0,0 +1,13 @@
+package system // import "github.com/docker/docker/pkg/system"
+
+import "syscall"
+
+// fromStatT converts a syscall.Stat_t type to a system.Stat_t type
+func fromStatT(s *syscall.Stat_t) (*StatT, error) {
+	return &StatT{size: s.Size,
+		mode: s.Mode,
+		uid:  s.Uid,
+		gid:  s.Gid,
+		rdev: s.Rdev,
+		mtim: s.Mtim}, nil
+}