`push` cannot push a 64-bit integer. In order to push it, we have
to first load a large integer to a register using `movabs` and then
push it to the stack.

Previously, chibicc's sizeof accepted only an expression, so you
couldn't write something like `sizeof(int)`. Now it accepts that.

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;