Enable native builds of szip via libaec

[mkitti]

szip is a compressor that can be built into HDF5. A free implementation of szip is available via libaec.

[mkitti]

After sorting out Windows, I may know how to convert everything to cmake now. That might be another pull request.

[saudet]

Why do we need to build libaec just for szip? Let's remove that dependency if we're not using it.

[mkitti]

How else do you propose building szip? Basically libaec provides a compatability layer that provides a szip interface.

szip itself is otherwise provided via a non-free license.

[saudet]

Ah, yes, I remember. So it doesn't matter if we use it via libaec, it's still not free and it's just libaec not being compliant isn't?

[mkitti]

As far as I know the license of libaec is https://gitlab.dkrz.de/k202009/libaec/-/blob/master/LICENSE.txt . It only provides the SZIP API and does not use any code from proprietary SZIP as far as I know.

https://gitlab.dkrz.de/k202009/libaec/-/blob/master/README.SZIP

Libaec includes a free drop-in replacement for the SZIP
library[1]. Just replace SZIP's shared library libsz.so* with
libaec.so* and libsz.so* from libaec. For Windows the DLLs are called
SZIP.DLL and AEC.DLL. Code which is dynamically linked with SZIP such
as HDF5 should continue to work with libaec. No re-compilation
required.

[mkitti]

According to NASA, there are no known patents on this standard compression either.

https://public.ccsds.org/Pubs/121x0b3.pdf

At time of publication, the specifications of this Recommended Standard are not known to be
the subject of patent rights. There is currently no known active patent for this standard.2

[mkitti]

Thank you for the edits and the merge!