Use nanosleep(2) instead of usleep(3)

usleep(3) was declared obsolete in POSIX.1-2001 and removed in
POSIX.1-2008 and nanosleep(2) was recommended to be used instead.

code/sys/sys_unix.c

@@ -38,6 +38,7 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 #include <fcntl.h>
 #include <fenv.h>
 #include <sys/wait.h>
+#include <time.h>
 
 qboolean stdinIsATTY;
 
@@ -548,11 +549,15 @@ void Sys_Sleep( int msec )
 	}
 	else
 	{
+		struct timespec req;
+
 		// With nothing to select() on, we can't wait indefinitely
 		if( msec < 0 )
 			msec = 10;
 
-		usleep( msec * 1000 );
+		req.tv_sec = msec/1000;
+		req.tv_nsec = (msec%1000)*1000000;
+		nanosleep(&req, NULL);
 	}
 }