macro expansion is not correct

```shell
chibicc -E macro.c
```

will get

```text
BAR() 1
```

however

```shell
gcc -E macro.c
```

will get

```text
BAR_I ()() 1 1 1
```

```c
// macro.c
#define EMPTY()
#define DEFER(id) id EMPTY()
#define EXPAND(...) __VA_ARGS__
#define BAR_I() BAR
#define BAR()  DEFER(BAR_I)()() 1
EXPAND(EXPAND(BAR()))
```