vendor: update buildkit to v0.8

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

vendor/github.com/moby/buildkit/solver/errdefs/op.go

@@ -0,0 +1,20 @@
+package errdefs
+
+import "github.com/moby/buildkit/solver/pb"
+
+type OpError struct {
+	error
+	Op *pb.Op
+}
+
+func (e *OpError) Unwrap() error {
+	return e.error
+}
+
+func WithOp(err error, iface interface{}) error {
+	op, ok := iface.(*pb.Op)
+	if err == nil || !ok {
+		return err
+	}
+	return &OpError{error: err, Op: op}
+}