Revert "Disable mpi-hs, #5444"
Revert "Disable mpi-hs, #5444"

This reverts commit 91d928d36c1c50d3d36676336ca622d9c19dcca2.

soenkehahn/stackage,massysett/stackage,mrkkrp/stackage,Daniel-Diaz/stackage,simonmichael/stackage,jonschoning/stackage,fpco/stackage,michalkonecny/stackage,iand675/stackage,clinty/stackage