Fix for dual operand form of fistp, also make reg ST(0) explicit and fix lindquists previous code that allowed dual operand form of fstp but dissallowed the single operand form accidently

module tangotests.sync2;

class Lock
{
}

const Lock lock;

static this()
{
    lock = new Lock;
}

void main()
{
    size_t id;
    synchronized(lock) id = 2;
}