[PATCH][AArch64] Fix PR87511

[Richard Sandiford]

Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> As mentioned in PR87511, the shift used in aarch64_mask_and_shift_for_ubfiz_p
> should be evaluated as a HOST_WIDE_INT rather than int.
>
> Passes bootstrap, OK for commit and backport?

OK for both, thanks.

Richard

(Reviewing since this is really an rtl handling bug rather than
something that needs port knowledge...)