port r11793 from 1.1: Flush output at each line, to be able to check out progression

tests/microbenchs/tasks_size_overhead.c

@@ -223,6 +223,7 @@ int main(int argc, char **argv)
 		starpu_shutdown();
 
 		FPRINTF(stdout, "\n");
+		fflush(stdout);
 	}
 
 	free(tasks);