glsl: Add ir node for barrier

v2:
 * Changes suggested by mattst88

[jordan.l.justen@intel.com: Add nir support]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>

src/glsl/ir_print_visitor.cpp

@@ -573,5 +573,10 @@ ir_print_visitor::visit(ir_end_primitive *ir)
    fprintf(f, "(end-primitive ");
    ir->stream->accept(this);
    fprintf(f, ")\n");
-
+}
+
+void
+ir_print_visitor::visit(ir_barrier *ir)
+{
+   fprintf(f, "(barrier)\n");
 }