[patch] Correct range checking in mallopt/mxfast/tcache [BZ #25194]

[DJ Delorie]

Jonathan Nieder <jrnieder@gmail.com> writes:
>     change (though it also makes me wonder if the tunable interface
>     could change to allow these to return void).

Amusingly, I'm pondering swbz 25035 where tunables fail completely due
to sbrk() failure, with absolutely no indication to the user :-(

Hiding failures from the user is bad.

> It also makes me wonder: should we propagate the return value from the
> other do_set_* calls in mallopt?  Even if they always succeed, this
> seems less error-prone in case they're changed later to not always
> succeed.

Perhaps.