Extension-based device info check
Extension-based device info check

Introduce a variant of POCL_RETURN_DEVICE_INFO_WITH_IMPL_CHECK that
only complains for null values if support for a specific extension is
claimed, and use it when returning the default and native vector widths
for the half type when cl_khr_fp16 is not supported.

Signed-off-by: Giuseppe Bilotta <6010d7f2c049984f25cd19568d4ace2cc46b0817@gmail.com>

franz/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl,pocl/pocl,pocl/pocl,pocl/pocl,Oblomov/pocl,franz/pocl,Oblomov/pocl,franz/pocl,franz/pocl,pocl/pocl,pocl/pocl,Oblomov/pocl