tools/io_uring: fix Makefile for pthread library link

Currently fails with:

io_uring-bench.o: In function `main':
/home/axboe/git/linux-block/tools/io_uring/io_uring-bench.c:560: undefined reference to `pthread_create'
/home/axboe/git/linux-block/tools/io_uring/io_uring-bench.c:588: undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
Makefile:11: recipe for target 'io_uring-bench' failed
make: *** [io_uring-bench] Error 1

Move -lpthread to the end.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/io_uring/Makefile

@@ -8,7 +8,7 @@ all: io_uring-cp io_uring-bench
 	$(CC) $(CFLAGS) -o $@ $^
 
 io_uring-bench: syscall.o io_uring-bench.o
-	$(CC) $(CFLAGS) $(LDLIBS) -o $@ $^
+	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
 
 io_uring-cp: setup.o syscall.o queue.o