These are the packages that would be merged, in order:

Calculating dependencies ...

!!! Problem resolving dependencies for =sci-libs/hdf5-2.2.0
 done!
Dependency resolution took 0.82 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=sci-libs/hdf5-2.2.0" has unmet requirements.
- sci-libs/hdf5-2.2.0::gentoo USE="hl threads zlib -cxx -debug -fortran -mpi -szip -test -unsupported"

  The following REQUIRED_USE flag constraints are unsatisfied:
    !unsupported? ( threads? ( !hl ) )

  The above constraints are a subset of the following complete expression:
    !unsupported? ( at-most-one-of ( cxx mpi ) threads? ( !cxx !mpi !fortran !hl ) )