glsl: Add ir_variable fields for explicit bindings.

These are not used yet, but they exist and are copied appropriately.

v2: Add an explicit "int binding" variable rather than reusing
    constant_value, as suggested by Paul Berry.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
2 files changed