i965/nir: Support barrier intrinsic function

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>

src/mesa/drivers/dri/i965/brw_fs_nir.cpp

@@ -1575,6 +1575,10 @@ fs_visitor::nir_emit_intrinsic(const fs_builder &bld, nir_intrinsic_instr *instr
       break;
    }
 
+   case nir_intrinsic_barrier:
+      emit_barrier();
+      break;
+
    default:
       unreachable("unknown intrinsic");
    }