Check that _Float16 is available before using it in openblas_config.h

Check that _Float16 is available before using it in openblas_config.h

Origin: upstream, https://github.com/OpenMathLib/OpenBLAS/commit/dc32a8a90f6e9169a6444826fcd55e0645db708c
                  https://github.com/OpenMathLib/OpenBLAS/commit/e926bb0523f1d001948a2214f213ec766d5d4414
Bug: https://github.com/OpenMathLib/OpenBLAS/issues/5747
Reviewed-by: Sébastien Villemot <sebastien@debian.org>
Last-Update: 2026-04-08

Fixes development package on armhf, s390x and sparc64.
Last-Update: 2026-04-08
Gbp-Pq: Name _Float16-redux.patch