Adds support for several conflicts between aflags and xax on x86: failing to reserve xax due to lazy aflags still residing in xax; failing to reserve aflags if xax is taken; and failing to get the app aflags value if xax is taken. For the first one, we throw away the lazy aflags. For the other two, we reserve a temporary scratch register, xchg it with xax, and restore it afterward. We place aflags in TLS and do not try to keep it in a register.
Issue: #511