Implement __wasi_fd_fdstat_get for Windows.

This commit fully implements `__wasi_fd_fdstat_get` on Windows so that
the descriptor flags can be determined.

It does this by calling into `NtQueryInformationFile` (safe to call from
user mode) to get the open mode and access of the underlying OS handle.

`NtQueryInformationFile` isn't included in the `winapi` crate, so it is
manually being linked against.

This commit also fixes several bugs on Windows:

* Ignore `__WASI_FDFLAG_NONBLOCK` by not setting `FILE_FLAG_OVERLAPPED`
  on file handles (the POSIX behavior for `O_NONBLOCK` on files).
* Use `FILE_FLAG_WRITE_THROUGH` for the `__WASI_FDFLAG_?SYNC` flags.
* `__WASI_FDFLAG_APPEND` should disallow `FILE_WRITE_DATA` access to
  force append-only on write operations.
* Use `GENERIC_READ` and `GENERIC_WRITE` access flags.  The
  latter is required when opening a file for truncation.

crates/wasi-common/winx/src/ntdll.rs

@@ -0,0 +1,65 @@
+//! Module for importing functions from ntdll.dll.
+//! The winapi crate does not expose these Windows API functions.
+
+#![allow(nonstandard_style)]
+
+use std::ffi::c_void;
+use std::os::raw::c_ulong;
+use std::os::windows::prelude::RawHandle;
+use winapi::shared::ntdef::NTSTATUS;
+use winapi::um::winnt::ACCESS_MASK;
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub(crate) enum FILE_INFORMATION_CLASS {
+    FileAccessInformation = 8,
+    FileModeInformation = 16,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub(crate) union IO_STATUS_BLOCK_u {
+    pub Status: NTSTATUS,
+    pub Pointer: *mut c_void,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub(crate) struct IO_STATUS_BLOCK {
+    pub u: IO_STATUS_BLOCK_u,
+    pub Information: *mut c_void,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub(crate) struct FILE_ACCESS_INFORMATION {
+    pub AccessFlags: ACCESS_MASK,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub(crate) struct FILE_MODE_INFORMATION {
+    pub Mode: c_ulong,
+}
+
+impl Default for IO_STATUS_BLOCK {
+    #[inline]
+    fn default() -> Self {
+        unsafe { std::mem::zeroed() }
+    }
+}
+
+#[link(name = "ntdll")]
+extern "C" {
+    // https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/nf-ntifs-ntqueryinformationfile
+    pub(crate) fn NtQueryInformationFile(
+        FileHandle: RawHandle,
+        IoStatusBlock: *mut IO_STATUS_BLOCK,
+        FileInformation: *mut c_void,
+        Length: c_ulong,
+        FileInformationClass: FILE_INFORMATION_CLASS,
+    ) -> NTSTATUS;
+
+    // https://docs.microsoft.com/en-us/windows/win32/api/winternl/nf-winternl-rtlntstatustodoserror
+    pub(crate) fn RtlNtStatusToDosError(status: NTSTATUS) -> c_ulong;
+}