sched.hh: add missing include

sched.hh now uses strlcpy(), which is defined in <string.h> so we should
include it directly instead of hoping that the code including sched.hh
will also include string.h.

Refs #1022.

Signed-off-by: Nadav Har'El <[email protected]>

include/osv/sched.hh

@@ -25,6 +25,7 @@
 #include <osv/rcu.hh>
 #include <osv/clock.hh>
 #include <osv/timer-set.hh>
+#include <string.h>
 
 typedef float runtime_t;