[mc] Add stack-cleaning compiler wrappers

This compiler wrappers clear each satck frame before using it in order
to avoid issues with unitialized variables in SimGridMC state
comparison.

Compiling with those compiler is much slower.
[mc] Do nto clean the main stack

We only need to clean the stacks of the application processes.
Otherwise, we spend a *lot* of time cleaniong the stack in the MC code
which slows SimGridMC a lot and is useless anyway.

The way we check if we need to clean the stack is currently quite
haskish and could be improved.
[mc] Fix the previous stack-cleaning optimisation
Add MPI_Info_* support.
This adds MPI_Info_create, MPI_Info_free, MPI_Info_get, MPI_Info_dup, MPI_Info_delete, MPI_Info_get_nkeys, MPI_Info_get_nthkey, MPI_Info_get_valuelen functions.
This is just basically a xbt dict wrapper.

We may have issues with the get_nthkey, as the xbt dict does not really keep the order.. but this mpi call is hum ... stupid? aniway.
Add mpich3 tests for MPI_Info calls.
As expected, the get_nthkey does not behave as expected, and it won't.
revalidate a tesh output