glsl/st: move st_nir_opts() into gl compiler common code

This will allow us to use this in future NIR linker work. It also makes
more sense to move it here as the classic drivers are gone, tgsi is
going away and we are merging more of the st into the gl common code.

Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14785>

src/compiler/glsl/gl_nir_linker.h

@@ -42,6 +42,8 @@ struct gl_nir_linker_options {
                                                 nir_var_mem_ssbo | \
                                                 nir_var_image)
 
+void gl_nir_opts(nir_shader *nir);
+
 bool gl_nir_link_spirv(const struct gl_constants *consts,
                        struct gl_shader_program *prog,
                        const struct gl_nir_linker_options *options);