On non-GNU systems (BSD/MacOS) there is no uname -o.
Suppress the failure message on these systems in the
call to set CT_SYS_OS (uname -s actually sets this variable).
yann.morin.1998@anciens.enib.fr: remove 'uname -o' altogether.
(transplanted from acae437fddccd7681c93a3b6c999c0796693d625)