bounded-pointer flag

[Nix]

On 11 Mar 2009, JohnT verbalised:
> There's a library called libsafe that is made to over-write certain i/o
> functions to prevent buffer over-runs, etc. If that can be built into
> glibc as an option by a bounds-checking setting, that might be nice to have.

This is likely better put in -D_FORTIFY_SOURCE, which already does
something fairly like this.

(and this probably belongs on libc-help@; moved there.)