[PATCH] explicit_bzero really final

[Florian Weimer]

* Zack Weinberg:

> Incorporates Florian's changes.  I intend to check this in tomorrow
> evening if there are no objections.  A build-many-glibcs test cycle is
> running now.

Thanks, let's do this.

I'm not completely happy with the text in the manual, but we can
revisit this topic once GCC gains support for explicit_bzero in some
form, and we better understand the implications.