Let `#define`d functions on 32-bit have same signatures as on 64-bit.

[IslandUsurper]

Because Rust treats isize and i32 as different types even when they are the same size, aliasing SetWindowLongPtrW to SetWindowLongW doesn't work without a cast. So, let's do the cast in winapi on x86.

[retep998]

This is a breaking change that will have to be postponed until the next major version.

[IslandUsurper]

@retep998, should I redo this PR against master, then?

[retep998]

No, because that is not what master is for (and also I can change what branch a PR is against anyway, no need to recreate PRs).

[micwoj92]

This branch has conflicts that must be resolved