ir_reader: Don't initialize globals, builtins, or constructors.

All of these are currently emitted as part of the IR, so by initializing
them, we actually end up with two copies.  For constructors, we may
eventually wish to avoid emitting them as part of the IR output.

ir_reader.cpp

@@ -63,9 +63,11 @@ _mesa_glsl_read_ir(_mesa_glsl_parse_state *state, exec_list *instructions,
    printf("\n-------------\n");
    
    _mesa_glsl_initialize_types(state);
-   _mesa_glsl_initialize_variables(instructions, state);
-   _mesa_glsl_initialize_constructors(instructions, state);
-   _mesa_glsl_initialize_functions(instructions, state);
+
+   /* FINISHME: Constructors probably shouldn't be emitted as part of the IR.
+    * FINISHME: Once they're not, remake them by calling:
+    * FINISHME: _mesa_glsl_initialize_constructors(instructions, state);
+    */
 
    read_instructions(state, instructions, expr, NULL);
 }