BUILD/MINOR: cpuset freebsd build fix

Add missing strings.h header. Required for ffsl definition used by
CPU_FFS macro.

This must be backported up to 2.4.

(cherry picked from commit 5592c7b455dc89584e1241f3952ca5e5c9fbf687)
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed