Do not run Eva without warning when the Ivette component is open.

- Add `mp_bitcnt_t` type;
- Add `__gmpz_mul_2exp()` (resp. `__gmpz_tdiv_2exp()`) to support left shift (resp. right shift);
- Add `__gmpz_fits_ulong_p()` and `__gmpz_fits_slong_p()` to guard GMP to C integer coercions.

The option `-machdep` should be called with `-e-acsl-prepare` before the
`-then`, otherwise when `-machdep` is finally used then the project is cleared
and all previous analysis are lost.