Fix OpenCL buils with 3.0 without subgroup support
Previously we assumed subgroup support is available with OpenCL >=v2.1 but v3.0 made this optional, so the check needed a fix for compilation to succeed e.g. on NVIDIA.
Edited by Szilárd Páll
Previously we assumed subgroup support is available with OpenCL >=v2.1 but v3.0 made this optional, so the check needed a fix for compilation to succeed e.g. on NVIDIA.