sys/acct.h: Add sys/types.h include

There's no harm in including sys/types.h here and acct.h needs it. This
file isn't defined by any standard, so what we do here wrt namespaces
likely doesn't matter. If it does, it will be easy enough to add the
necessary __BSD_VISIBLE guards in the future.

Sponsored by: Netflix

(cherry picked from commit b194db935565d58392c21906419cbd99a5ecc0c3)