math/openblas64: new port, OpenBLAS with 8 byte integers

Remark 1: CMake support is experimental. It does not yet support all build
options, but the 64 bits libraries can be installed without conflict with the
classic version.

Remark 2: some tests fail on -CURRENT "SIGSEGV: Segmentation fault -
invalid memory reference.". It seems caused by clang-18 and threads.