Bug#924712: crypt() not available _XOPEN_SOURCE is defined

[Florian Weimer <fw@deneb.enyo.de>]

* Laurent Bigonville:

> Package: libc6-dev
> Version: 2.28-8
> Severity: serious
>
> Hi,
>
> The crypt.3 manpage, state that _XOPEN_SOURCE should be define for
> crypt() to be available.
>
> But it looks that it's currently the opposite, if _XOPEN_SOURCE is
> defined, the function cannot be found.

Can you compile the software using _DEFAULT_SOURCE (well, the default)
or _GNU_SOURCE instead?

We do not want to provide the CRYPT extension anymore because it
implies not just support for the crypt function, but also for the DES
encryption functions, which definitely do not want.  In _XOPEN_SOURCE
mode, it's either all of these functions or none of them (and we chose
the latter because of DES), otherwise glibc wouldn't conform to the
interface specification.

We definitely should update the manual page, though.