Adding a MACHINE_ARCH note

[Kurt Lidl]

> On Jul 10, 2013, at 03:08, Peter Wemm <peter at wemm.org> wrote:
>> On Tue, Jul 9, 2013 at 5:56 PM, Adrian Chadd <adrian at freebsd.org> wrote:
>>> ... boy I'd like to see this particular x86 hiccup fixed before this
>>> stuff is mainstream.
>>
>> I'm not entirely sure how much support there is behind "x32".  I don't
>> know if its much more than an academic curiosity or if there's real
>> demand for it.
>
> It seems to be driven by Intel and Google.  The idea is that for some
> applications (or maybe even most :), an ILP32 model will perform better.

I believe that Google's NaCl (native client) plugins for Chrome all use
the "x32" ABI.  The NaCl stuff uses this, along with a "safe" code
generation path to implement part of the sandboxing for Chrome plugins.

Ultimately, to have a fully functioning Chrome (with plugins) on amd64
hosts, we'll want to support "x32".

-Kurt