Make the GP executable work with SAGE_DEBUG on Darwin

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/13921">trac #13921</a>.

Diff for the PARI spkg, for review only

Reported by: SimonKing

Component: number theory

CC: jdemeyer

Report Upstream: Reported upstream. No feedback yet.

Authors: Jeroen Demeyer

Dependencies: 

Work issues: 

Reviewers: Volker Braun

Merged in: sage-5.6.rc0

Attachments: <ol><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/13921/pari-2.5.3.p2.diff">pari-2.5.3.p2.diff: Diff for the PARI spkg, for review only</a> by jdemeyer at 20130107T15:30:30</li></ol>