OpenBLAS requires additional casts due to header differences

[Micket]

Trying to link against OpenBLAS fails because cblas_cgemm, cblas_zgemm, cblas_zgemv, cblas_cgemv, cblas_zdot, cblas_cdot, uses const double * and const float * instead of const void *.

Any cast from std::complex<float/double> will fail.

Explicit downcasting to const double * and const float * would be a workaround.

[Micket]

I found that OpenBLAS had already resolved the inconsistency on their end: OpenMathLib/OpenBLAS#1322
though, there still aren't any releases with this fix.

Unfortunately, it also doesn't seem like it would be a nice workaround solution until then either, because of cblas_*dotu_sub forcing a openblas-specific struct as the output value parameter.
This would require a OpenBLAS specific check.

[shiozaki]

I think this is OpenBlas problem (I think use of double* is simply wrong), and therefore, we do not make a workaround on the bagel side. In addition, OpenBlas should be compiled with ""-ff2c"" flag so that zdotu/zdotc signatures will be the same as what are assumed in BAGEL.

In general, we will not introduce any Blas-implementation-specific fixes in BAGEL. Let me close for the time being - if you have additional information, let me know.