Double-Down and Embree are disabled in Cardinal submodule by default

[simopier]

Reason

Double-Down and Embree are disabled in Cardinal submodule by default to avoid current build issues (see neams-th-coe/cardinal#1142).
However, whenever these things are fixed in Cardinal, it could also be fixed in SALAMANDER.

Design

Follow up with the status of Double-Down and Embree in Cardinal and update SALAMANDER when possible.

Impact

More general build

[simopier]

See #85 for context.

[loganharbour]

We shouldn't need double down. It's not a default in cardinal anymore.

[cticenhour]

Correct - but I was also under the impression that this was due to intermittent build issues on certain platforms. Sounded like they leave the door open on re-enabling it. We can eventually delete this issue if that never arises.

[nuclearkevin]

To provide some context, the build issue we are dealing with when using Double-Down + Embree4 has to do with Double-Down failing to build when an external HDF5 directory is specified (which is necessary when building Cardinal in the MOOSE conda environment). Once I get around to fixing that we'll likely enable Double-Down by default, as the improvement to per-thread performance and threaded scalability is substantial when running OpenMC with CAD geometry.

I'll drop a message here when we make that change, alongside any buildsystem changes that were necessary to get Double-Down working in the MOOSE conda environment.

[cticenhour]

Thanks @nuclearkevin!

The issue you were having with external HDF5 wouldn't happen to look similar to an issue I was having, would it? I'll link the comment:

#85 (comment)

I didn't have time to pull on any threads to find a resolution, but did find a couple of hacky local workarounds on my own Mac.

[nuclearkevin]

Unfortunately we're running into a different HDF5 error. CMake throws a fit when attempting to build Double-Down with an externally provided HDF5 library:

CMake Error at CMakeLists.txt:72 (add_library):
  Target "dd" links to target
  "-L/home/kevincs2/Projects/new_cardinal/install/lib -lMOAB
  hdf5::hdf5-shared" but the target was not found.  Perhaps a find_package()
  call is missing for an IMPORTED target, or an ALIAS target is missing?

It's a little odd since Double-Down only depends on HDF5 through MOAB, and MOAB builds with no issues...