`OPENBLAS_XXX` cross compile options aren't respected under linux

[mlaventure]

While trying to cross-compile as a dependency of a project under the Yocto Project environment, I was surprised to realize that the OPENBLAS_CC and friends are not used when building for linux.

Is this intended? The README clearly states that those are meant to be used for cross-compiling. Should openbas-build be updated to respect those variables?

[ivan-aksamentov]

The system with cherry-picked renamed env vars is needlessly complex, broken and cannot keep up with upstream updates. Env vars should be passed as is. Half of the code in these crates can be removed.