nir: Add native_integers to nir_shader_compiler_options.

nir: Add native_integers to nir_shader_compiler_options.

glsl_to_nir, tgsi_to_nir, and prog_to_nir all want to know whether the
driver supports native integers.  Presumably other passes may as well.

Adding this to nir_shader_compiler_options is an easy way to provide
that information, as it's accessible via nir_shader::options.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>