Updates about BLAS64

[Mo Zhou <lumin@debian.org>]

Hi -science,

Some time ago we discussed about packages for BLAS64 ABI/API.
Here are some updates about the subsequent works:

* blas64 and lapack64 symlinks and alternatives have been added to intel-mkl.

   src:intel-mkl
     bin:libmkl-rt
       enhances: libblas.so.3, libblas64.so.3, liblapack.so.3, liblapack64.so.3
       alternative: libblas64.so.3 -> libmkl_rt.so
                    liblapack64.so.3 -> libmkl_rt.so
                    ...
     bin:libmkl-dev
       enhances: libblas64.so, liblapack64.so, ...
       alternative: libblas64.so -> libmkl_rt.so
                    liblapack64.so -> libmkl_rt.so

* A new BLAS implementation called BLIS[1] is nearly ready to upload.
  This is likely the first package that will provide 64bit BLAS API/ABI
  in main section of our archive.

  BLIS supports three different threading models, just like openblas.
  The difference is that, BLIS will be compiled 6 times with different
  configurations:

  (openmp, pthread, serial) x (32-bit, 64-bit) = 6 combinations

  BLIS shared libraries with different threading models and the same
  index length cannot coexist. Any 32-bit lib can co-exist with any
  64-bit one.

   src:blis
     bin:libblis1 (meta)
       deps: libblis1-openmp | libblis1-pthread | libblis1-serial
       provides: libblas.so.3
     bin:libblis64-1 (meta)
       deps: libblis64-1-openmp | ...
       provides: libblas64.so.3
     ...

  Note that BLIS doesn't provide LAPACK implementation.

  @Sebastian: Does this look good to OpenBLAS?

[1] https://salsa.debian.org/science-team/blis