Fix race condition rebuilding MPIR,... with GCC spkg

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/14168">trac #14168</a>.



Reported by: jdemeyer

Component: build

CC: kcrisman,, leif

Report Upstream: N/A

Authors: Jeroen Demeyer

Dependencies: 

Work issues: 

Reviewers: Karl-Dieter Crisman, Leif Leonhardy

Merged in: sage-5.8.beta3

Attachments: <ol><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/14168/14168_serial_gcc.patch">14168_serial_gcc.patch: </a> by jdemeyer at 20130302T11:10:30</li></ol>