vendor: add buildkit

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

vendor/github.com/tonistiigi/fsutil/diff.go

@@ -0,0 +1,45 @@
+package fsutil
+
+import (
+	"context"
+	"hash"
+	"os"
+
+	"github.com/tonistiigi/fsutil/types"
+)
+
+type walkerFn func(ctx context.Context, pathC chan<- *currentPath) error
+
+func Changes(ctx context.Context, a, b walkerFn, changeFn ChangeFunc) error {
+	return nil
+}
+
+type HandleChangeFn func(ChangeKind, string, os.FileInfo, error) error
+
+type ContentHasher func(*types.Stat) (hash.Hash, error)
+
+func GetWalkerFn(root string) walkerFn {
+	return func(ctx context.Context, pathC chan<- *currentPath) error {
+		return Walk(ctx, root, nil, func(path string, f os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+
+			p := &currentPath{
+				path: path,
+				f:    f,
+			}
+
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case pathC <- p:
+				return nil
+			}
+		})
+	}
+}
+
+func emptyWalker(ctx context.Context, pathC chan<- *currentPath) error {
+	return nil
+}