glsl: Exclude ir_var_hidden variables from the program resource list.

glsl: Exclude ir_var_hidden variables from the program resource list.

We occasionally generate variables internally that we want to exclude
from the program resource list, as applications won't be expecting them
to be present.

The next patch will make use of this.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>