Applied fix contributed by Greg King.

The code
  void foo(void)
  {
    int i;
    long l = 1L * i;
  }
triggered an
  Internal compiler error:
  Code generation messed up: StackPtr is -4, should be -2

Greg King: "We are lucky that the bug is simple -- a missing "else".  The result is that the compiler thinks that it does the opposite of what it actually does:  It thinks that it pushes the non-constant expression onto the stack. It doesn't; so, cc65's stack pointer is wrong."