FindHDF5 does not set required MPI dependency
When HDF5_PARALLEL is set, it is required to link against libmpi (and potentially libmpixx) but the Module does not do that.
I found that invoking the HDF5 compiler wrapper with
-show (as done by the Module) unwraps only 1 layer and shows mpicc as the compiler while
--show also unwraps the mpicc wrapper and shows all required libraries.