CMake build fails on Windows when prefix flag is used

[Harishmcw]

When building OpenBLAS with CMake and using a custom prefix (e.g., scipy_), the build fails with undefined symbol errors:

lld-link: error: <root>: undefined symbol: shgemm_
lld-link: error: <root>: undefined symbol: shgemv_
lld-link: error: <root>: undefined symbol: cblas_shgemm

Observed behavior:

These symbols (shgemm_, shgemv_, cblas_shgemm) are conditionally compiled only when BUILD_HFLOAT16=ON. However, even when this flag is OFF, the generated renamesys.def file still contains entries like:

scipy_shgemm=shgemm_ @XX
scipy_shgemv=shgemv_ @YY
scipy_cblas_shgemm=cblas_shgemm @ZZ

Because the corresponding object files (shgemm.obj, etc.) are not built, the linker fails to find these symbols, resulting in the errors above.
When BUILD_HFLOAT16=ON, the objects are built and the build completes successfully.

Expected behavior:

When BUILD_HFLOAT16=OFF, the .def file should not include the shgemm, shgemv, or cblas_shgemm symbols.

[martin-frbg]

Right, looks like the BUILD_HFLOAT16 is missing in the recently added CMakeLists.txt code that generates the DLL