enable building the cblas64 library

[epsilon-0]

changes all function signatures to use CBLAS_INDEX
also fixes internal variables to be CBLAS_INDEX
all tests are passing

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A lot of the optimized implementations are providing an implementation for CBLAS64
It is good to have the reference implementation also providing this, as we already have the 64 bit libraries for others.

I've followed your standard syntax rules from other files.
The variable name used is the standard CBLAS_INDEX which should keep it compatible with all other files.

Would be really awesome to finally have this reference implementation ❤️

Thanks a lot,
Aisha

[langou]

I am in favor of this PR.

[codecov]

Codecov Report

Merging #460 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #460   +/-   ##
=======================================
  Coverage   81.86%   81.86%           
=======================================
  Files        1863     1863           
  Lines      181096   181096           
=======================================
  Hits       148263   148263           
  Misses      32833    32833           

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[martin-frbg]

I'm certainly not against it either, even if it means losing one competitive advantage of OpenBLAS 😃
Just for cross-referencing: this is expected to fix both #459 and #184

[epsilon-0]

I'm certainly not against it either, even if it means losing one competitive advantage of OpenBLAS smiley
Just for cross-referencing: this is expected to fix both #459 and #184

XD
I'd say this is not going to make OpenBLAS lose an advantage.
In fact, I'd say this should actually be a positive note for OpenBLAS (and any other provider, like blis), because now it can even say that it provides an optimized reference CBLAS64 API, as opposed to providing a CBLAS64 API, as previously we did not have a standardized CBLAS64 API.

[epsilon-0]

@langou
thanks a lot for the quick merge!