Impala MPI bindings

So far this is only rudimentary. If you have need of more bindings, please add them and contribute any nicer wrappers you build.

Build and run

Make sure impala and clang are on the PATH.

Change the MPIStatus struct in src/mpi.impala if you're not using OpenMPI.

mkdir build
cd build
cmake .. -DAnyDSL_runtime_DIR:PATH="<add path to anydsl runtime here>/build/share/anydsl/cmake"
make

mpirun -n 2 src/main