Bug#770290: ping

[Dima Kogan]

Hi. Can we get this working? There're many packages that

  Build-Depends: (stuff that eventually depends on BLAS)

and those can't be cross-built right now.

The main proposal from #760936 was to manage a separate alternative for
each architecture. There's precedent for this at least in src:petsc and
src:s2tc.

I'm attaching a patch series that applies this idea here. The patches
mostly work. There're at least two bugs here that need to be dealt with,
and I can work on those. But in the meantime, let's decide that this is
the approach we want to pursue. The issues:


1. Something is wrong with libblas.a. It ends up mostly empty for me

2. There's now a separate set of alternatives for each arch called
something like blas-ARCH. Installing one of the new packages creates
these new alternatives, but doesn't remove the old alternatives, which
end up as a broken link.


Clearly, we'd also need to update the other packages that provide BLAS
implementations, but let's do this one step at a time.

dima
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