Add a missing "void" to the prototype for __cpuset_zero_s().
Reported-by: Marco Mason <marco.mason@gmail.com>
Addresses: https://cygwin.com/pipermail/cygwin/2023-September/254423.html
Signed-off-by: Mark Geisert <mark@maxrnd.com>
Fixes: c6cfc99648d6 (Cygwin: sys/cpuset.h: add cpuset-specific external functions)