Intel mpi comes with an installation of libfabric (which it needs as a
dependency). It can use other implementations of libfabric at runtime
though, so if you install a package that depends on `mpi` and
`libfabric`, you can specify `intel-mpi+external-libfabric` and ensure
that the Spack-built instance is used (both by `intel-mpi` and the
root).
Apply analogous change to intel-oneapi-mpi.
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