Fix ir_return cloning to actually use the cloned subexpression.

This caused a nasty bug where the function inliner would create new
variables for each of the formal parameters, but the body would still
reference the old copies.

This was highly visible since the dead code eliminator (rightly) removed
the new declarations, leading to printed IR that referenced non-existent
variable names.

ir_function_inlining.cpp

@@ -264,8 +264,7 @@ ir_function_cloning_visitor::visit(ir_return *ir)
    rval = this->result->as_rvalue();
    assert(rval);
 
-   result = new ir_assignment(new ir_dereference(this->retval),
-			      ir->get_value(), NULL);
+   result = new ir_assignment(new ir_dereference(this->retval), rval, NULL);
 }