windows: stat::st_mode and S_IFMT are of different type

[cgzones]

On windows stat::st_mode https://github.com/rust-lang/libc/blob/bac14427831aaff9b79dcdd125c03109414215c5/src/windows/mod.rs#L60 and S_IFMT (and other mode flags) https://github.com/rust-lang/libc/blob/bac14427831aaff9b79dcdd125c03109414215c5/src/windows/mod.rs#L146 are of different type, resulting in code like

fn is_regular(stat: &libc::stat) -> bool {
    stat.st_mode & libc::S_IFMT == libc::S_IFREG
}

to not be portable.

[joshtriplett]

We need to check if these are in fact different types in Windows headers, or if they're the same type and we have an error in the crate's types.

[ChrisDenton]

Here's the ucrt header.