Trac #17348: gcc 4.9.2 does not build on ARM

Upstream bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63740

Fixes it on our arm buildbot.

URL: http://trac.sagemath.org/17348
Reported by: vbraun
Ticket author(s): Volker Braun
Reviewer(s): Jean-Pierre Flori