vendor: update buildkit to v0.8

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

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

@@ -0,0 +1,41 @@
+package errdefs
+
+import (
+	fmt "fmt"
+
+	"github.com/containerd/typeurl"
+	"github.com/moby/buildkit/util/grpcerrors"
+)
+
+func init() {
+	typeurl.Register((*Subrequest)(nil), "github.com/moby/buildkit", "errdefs.Subrequest+json")
+}
+
+type UnsupportedSubrequestError struct {
+	Subrequest
+	error
+}
+
+func (e *UnsupportedSubrequestError) Error() string {
+	msg := fmt.Sprintf("unsupported request %s", e.Subrequest.Name)
+	if e.error != nil {
+		msg += ": " + e.error.Error()
+	}
+	return msg
+}
+
+func (e *UnsupportedSubrequestError) Unwrap() error {
+	return e.error
+}
+
+func (e *UnsupportedSubrequestError) ToProto() grpcerrors.TypedErrorProto {
+	return &e.Subrequest
+}
+
+func NewUnsupportedSubrequestError(name string) error {
+	return &UnsupportedSubrequestError{Subrequest: Subrequest{Name: name}}
+}
+
+func (v *Subrequest) WrapError(err error) error {
+	return &UnsupportedSubrequestError{error: err, Subrequest: *v}
+}