d/rules: add a static list of OPENMPI_ARCHITECTURES and MPICH_ARCHITECTURES,...

d/rules: add a static list of OPENMPI_ARCHITECTURES and MPICH_ARCHITECTURES, and export them in debian_defaults

This will need to be updated manually every time there is a new architecture
present, but it's the only way to have that interesting data in the final binary
package.

See https://lists.debian.org/20160215174941.GA29224@chase.mapreri.org for some
discussion about it.