Need support for `__ashrdi3`

[AngheloAlf]

GCC can emit a call for __ashrdi3 for a right shift between int64_t when using -Os. GCC won't emit this call when using -Ofast, but it can still be good to have.

To recreate:

long long __ll_rshift(long long left, long long right) {
    return left >> right;
}