Fix incorrect uname usage.

The POSIX function uname() can return any non-negative value for success.
- Example: Solaris 10 returns 1 on success.
See: http://pubs.opengroup.org/onlinepubs/009695399/functions/uname.html



Change-Id: Ic3d51f94a31d8b562b28a2d09df3d31b04c77dc8
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
(cherry picked from qtbase/e97c37a37ac27f9ab901e974f0a882e81ffd571d)
Reviewed-by: Daniel Teske <daniel.teske@digia.com>