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.

mesa/shader/prog_print.c

@@ -833,7 +833,7 @@ void
 _mesa_print_instruction(const struct prog_instruction *inst)
 {
    /* note: 4th param should be ignored for PROG_PRINT_DEBUG */
-   _mesa_fprint_instruction_opt(stderr, inst, 0, PROG_PRINT_DEBUG, NULL);
+   _mesa_fprint_instruction_opt(stdout, inst, 0, PROG_PRINT_DEBUG, NULL);
 }
 
 #if 0