Handle complex type declarations correctly

chibicc can now read complex type declarations such as below.

  long x;
  long int x;
  int long x;
  short x;
  short int x;
  int short x;
  long long x;
  long long int x;

In the following example, `x` is defined as an alias for `int`.

  typedef x;

Below is valid C code where the second `t` is a local variable
of type int having value 3.

  typedef int t;
  t t = 3;