Change xbt_strdup, xbt_malloc, xbt_malloc0 and xbt_realloc from macro to inline funct...

Change xbt_strdup, xbt_malloc, xbt_malloc0 and xbt_realloc from macro to inline functions. It shouldn't change anything in generated code, and that way, we don't have to use the 'malloc(n)?:die' construct, which troubles splint. Less macro should also make Oli happy, for example. Also move the gcc attribute wrapper to another file to kill circular dependencies

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@1099 48e7efb5-ca39-0410-a469-dd3cf9ba447f