Avoid using a version range for windows-sys; causes non-deterministic version resolution

[joshtriplett]

Cargo's version resolver doesn't handle version ranges like this very
well, resulting in non-deterministic flip-flopping of versions.

rust-lang/cargo#9029
rust-lang/cargo#5529
https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/Cargo.2Elock.20non-deterministically.20flipflopping/with/520024108

[BurntSushi]

Ref #19 and cc @ChrisDenton

[joshtriplett]

@BurntSushi The issue here is that this will often cause crates to use multiple versions of windows-sys when they otherwise wouldn't have, because cargo can't necessarily say "oh, if I used the latest version I'd only need one version". And not only that, but cargo will go back and forth between versions of windows-sys when doing other unrelated updates that cause a new resolve.

[ChrisDenton]

Hm, this is unfortunate. The thing is, it doesn't seem to matter if there's six months or a year between windows-sys releases, there will always be major crates that are a version or two behind.

If this is the better of the two options then I'm grudgingly ok with it. But maybe I should try to encourage more use of windows-bindgen. It feels wasteful for every project to be generating their own bindings but at this point I think it's the least worse option.

[BurntSushi]

I'm very open to using windows-bindgen. I think I just haven't had the time to sit down and do it.

[ChrisDenton]

Ok, I made #25 to see what that would look like.