Reduce dependencies on non-windows targets

[mexus]

Description

Depend on winapi crate only on windows target.

Motivation and Context

winapi is only required on windows target, but it is currently fetched even for "unix" platforms. With this PR merged, the amount of downloaded data is reduced significantly on non-windows targets.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

[Veetaha]

Hi, @yoshuawuyts, any chance to merge this?

[krojew]

bump