clang version influences __unix__

[Mats Erik Andersson <mats.andersson@gisladisker.se>]

Dear all,

by accident I just noticed that clang in version 1:3.0-6.2,
as present in Wheezy, fails to define either of 'unix',
'__unix', and '__unix__' when running on GNU/kFreeBSD.
However, on plain FreeBSD-9.0, clang version 3.0 does define
these as 1, which is to be expected.

With GNU/Linux version 1:3.2repack-11 all three macros
are correctly set to 1. How does this matter look in
GNU/kFreeBSD for sid/unstable?

There are a lot of software releases around that do rely
on the presence of at least __unix__ to function properly,
including GNU Inetutils where I mostly work.

Best regards,
  Mats Erik Andersson, DM