Move common functionality into hostcalls mod

src/sys/windows/hostcalls_impl/mod.rs

@@ -0,0 +1,10 @@
+//! Windows-specific hostcalls that implement
+//! [WASI](https://github.com/CraneStation/wasmtime-wasi/blob/wasi/docs/WASI-overview.md).
+mod fs;
+mod misc;
+
+use super::fdentry;
+use super::host_impl;
+
+pub(crate) use self::fs::*;
+pub(crate) use self::misc::*;