fix compiler warnings

src/core/disk.c

@@ -91,7 +91,7 @@ int starpu_disk_register(struct starpu_disk_ops *func, void *parameter, starpu_s
 
 	/* workers can manage disk memnode */
 	struct _starpu_machine_config *config = _starpu_get_machine_config();
-	int worker;
+	unsigned worker;
 	for (worker = 0; worker < starpu_worker_get_count(); worker++)
 	{
 		struct _starpu_worker *workerarg = &config->workers[worker];

src/core/workers.c

@@ -1735,7 +1735,7 @@ unsigned starpu_worker_is_blocked_in_parallel(int workerid)
 		 * another worker, we must avoid race conditions between
 		 * 'blocked' state changes and state observations. This is the
 		 * purpose of this 'if' block. */
-		cur_worker = cur_workerid<starpu_worker_get_count()?_starpu_get_worker_struct(cur_workerid):NULL;
+		cur_worker = cur_workerid<(int)(starpu_worker_get_count())?_starpu_get_worker_struct(cur_workerid):NULL;
 
 		relax_own_observation_state = (cur_worker != NULL) && (cur_worker->state_relax_refcnt == 0);
 		if (relax_own_observation_state && !worker->state_relax_refcnt)

src/debug/traces/starpu_fxt.c

@@ -2594,8 +2594,6 @@ static void handle_task_name(struct fxt_ev_64 *ev, struct starpu_fxt_options *op
 
 static void handle_task_done(struct fxt_ev_64 *ev, struct starpu_fxt_options *options)
 {
-	char *prefix = options->file_prefix;
-
 	unsigned long job_id;
 	job_id = ev->param[0];