#52 fix a GNU ar warning about deterministic mode

[Pete Batard]

• GNU ar currently produces the following string of warnings:
  Warning: Archive 'libefi.a' seems to have been created in deterministic mode.
  '<file>.o' will always be updated. Please consider passing the U flag to ar to avoid the problem.</file>
• This patch fixes the issue

[Nigel Croxon]

Thank you for the patch, Pete.

commit bd38ba4b6bd944986d148b923d26aa3069087a57