Wrong site_id in notify BB

[ercoppa]

The current code in gen_tb_start:

TCGv_i64 block = tcg_const_i64((uint64_t)tb);

uses as site_id the address of struct TB. This address does not reflect the address of the original BB. The resulting side effect is that the bitmap built by the SymCC runtime may be wrong: the address of the TB may change across runs.

One possible fix could this one. Let me know how to improve it.

[ercoppa]

This is the same issue reported by #10. Sorry for the duplicate entry. My fix is slightly cleaner.