Add support for wasi_snapshot_preview1. (#592)

* Add support for wasi_snapshot_preview1.

This adds support for the new ABI, while preserving compatibility
support for the old ABI.

* Fix compilation on platforms where nlink_t isn't 64-bit.

* rustfmt

* Fix Windows build errors.

crates/wasi-common/src/hostcalls/fs.rs

@@ -1,6 +1,6 @@
 #![allow(non_camel_case_types)]
 use crate::ctx::WasiCtx;
-use crate::{wasi, wasi32};
+use crate::{hostcalls_impl, wasi, wasi32};
 
 hostcalls! {
     pub unsafe fn fd_close(wasi_ctx: &mut WasiCtx, fd: wasi::__wasi_fd_t,) -> wasi::__wasi_errno_t;

crates/wasi-common/src/hostcalls/misc.rs

@@ -1,6 +1,6 @@
 #![allow(non_camel_case_types)]
 use crate::ctx::WasiCtx;
-use crate::{wasi, wasi32};
+use crate::{hostcalls_impl, wasi, wasi32};
 use log::trace;
 use wasi_common_cbindgen::wasi_common_cbindgen;