glsl: add gl_BoundingBox and associated varying slots

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/shader_enums.c

@@ -158,6 +158,8 @@ gl_varying_slot_name(gl_varying_slot slot)
       ENUM(VARYING_SLOT_PNTC),
       ENUM(VARYING_SLOT_TESS_LEVEL_OUTER),
       ENUM(VARYING_SLOT_TESS_LEVEL_INNER),
+      ENUM(VARYING_SLOT_BOUNDING_BOX0),
+      ENUM(VARYING_SLOT_BOUNDING_BOX1),
       ENUM(VARYING_SLOT_VAR0),
       ENUM(VARYING_SLOT_VAR1),
       ENUM(VARYING_SLOT_VAR2),