Try to produce the same results with minmin on different setups.

Use a volatile double temporary variable to avoid rounding differences
on 32bit or 64bit x86, with or without gcc optimizations.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@8557 48e7efb5-ca39-0410-a469-dd3cf9ba447f