Bug#972068: arpack: provide 64-bit (ILP64) build

[Mo Zhou]

On Mon, Oct 12, 2020 at 12:05:31PM +0800, Drew Parsons wrote:
> This would be an extra set of packages (e.g. libarpack2-64-dev,
> libarpack2-64) providing libarpack64.so (or libarpack-64.so) alongside
> libarpack.so (i.e. coinstallable).  It would be built against
> libblas64-dev instead of libblas-dev.

Maybe libarpack64-2-dev? The "64" is a part of SONAME. e.g. the packages
libblas64-dev, libblas64-3 are not named as something like
libblas3-64-dev and libblas3-64. Plus, our convension is that the last
number denotes the SOVERSION, right? And do we mean SOVERSION=64 by
libarpack2-64 (which I think definitely not).