ir_to_mesa: Print out the ir along with the Mesa IR.

ir_to_mesa: Print out the ir along with the Mesa IR.

Ideally this would be hooked up by ir_print_visitor dumping into a
string that we could include as prog_instruction->Comment when in
debug mode, and not try keeping ir_instruction trees around after
conversion to Mesa.  The ir_print_visitor isn't set up to do that for
us today.