Deferred expansion doesn't work correctly

Source code

```c
#define empty()
#define a() b empty()()
#define b() c empty()()
#define c() d empty()()
#define d() e empty()()
#define id(x) x

id(a())
```

Running `cpp` versus `pcpp`:

```bash
[tmp]$ cpp a.c
# 0 "a.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "a.c"
# 9 "a.c"
c ()
[tmp]$ pcpp a.c
#line 9 "a.c"
e ()
```