basic VRP min/max range overflow question

[DJ Delorie]

> Then, you will like the following kind of patches:
> 
> +      warning (0, "%H undefined behavior if loop runs for more than %qE iterations",
> +	       find_loop_location (loop), estimation);

I think we would like them better if you could choose to silence them,
especially when people use -Werror.  Please avoid passing 0 to
warning() for new warnings; especially if there's no other way to
control them.