Unnecessary cross-compilation for openblas-build

[gkobeaga]

In the process of cross-compiling, openblas-build is compiled to both host and target architectures, see #114. Building to the target architectures might not be necessary since openblas-build has its utilization exclusively for the download/build sequence of OpenBLAS.

As per my understanding, this happens because: 1) openblas-build is a build-dependency for openblas-src, so it is compiled to the host architecture; 2) it's a member of the virtual workspace, and it also ends up getting compiled to the target architecture.

One potential solution could be to remove openblas-build from the workspace. Stripping it away would result in a virtual workspace containing a single crate. Consequently, the logical step would be to move openblas-src to the root.