build: enabled passing the MPI standard to the source (BUD_MPI)
build: enabled passing the MPI standard to the source (BUD_MPI)

Signed-off-by: Nick Papior <81a73bca3d342ffee33d7cf845fdbf77b6553831@gmail.com>

siesta-project/refype,siesta-project/refype,siesta-project/buds