vendor: update buildkit to v0.8

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

vendor/github.com/Microsoft/hcsshim/internal/winapi/errors.go

@@ -0,0 +1,15 @@
+package winapi
+
+import "syscall"
+
+//sys RtlNtStatusToDosError(status uint32) (winerr error) = ntdll.RtlNtStatusToDosError
+
+const (
+	STATUS_REPARSE_POINT_ENCOUNTERED               = 0xC000050B
+	ERROR_NO_MORE_ITEMS                            = 0x103
+	ERROR_MORE_DATA                  syscall.Errno = 234
+)
+
+func NTSuccess(status uint32) bool {
+	return status == 0
+}