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/helpers.rs

@@ -14,7 +14,7 @@ pub(crate) fn systemtime_to_timestamp(st: SystemTime) -> Result<u64> {
 /// Creates not-owned WASI path from byte slice.
 ///
 /// NB WASI spec requires bytes to be valid UTF-8. Otherwise,
-/// `__WASI_EILSEQ` error is returned.
+/// `__WASI_ERRNO_ILSEQ` error is returned.
 pub(crate) fn path_from_slice<'a>(s: &'a [u8]) -> Result<&'a str> {
     str::from_utf8(s).map_err(|_| Error::EILSEQ)
 }