Require Linux 3.2 except on x86 / x86_64, 3.2 headers everywhere

[Florian Weimer]

* Joseph Myers:

> In the discussion in February, some concerns were expressed about
> compatibility with OpenVZ containers.  It's not clear that these are
> real issues, given OpenVZ backporting kernel features and faking the
> kernel version for guest software, as discussed in
> <https://sourceware.org/ml/libc-alpha/2016-02/msg00278.html>.  It's
> also not clear that supporting running GNU/Linux distributions from
> late 2016 (at the earliest) on a kernel series from 2009 is a sensible
> expectation.  However, as an interim step, this patch increases the
> requirement everywhere except x86 / x86_64 (since the controversy was
> only about those architectures); the special caveats and settings can
> easily be removed later when we're ready to increase the requirements
> on x86 / x86_64 (and if someone would like to raise the issue on LWN
> as suggested in the previous discussion, that would be welcome).  3.2
> kernel headers are required everywhere by this patch.

Agreed, let's do it this way.