Having a quick look at efsw, it depends on both libc and the windows API, both are huge dependencies. The Rust bindings for libc come to about 122 thousand lines, while the winapi crate is about 180 thousand lines.
[Edit] And for completeness, Microsoft's Windows crate is 630 thousand lines, though that goes way beyond simple bindings, and actually provides wrappers to make its use more idiomatic.
[Edit] And for completeness, Microsoft's Windows crate is 630 thousand lines, though that goes way beyond simple bindings, and actually provides wrappers to make its use more idiomatic.