Implement fd_fdstat_set_flags for Windows.

This commit implements `fd_fdstat_set_flags` for Windows.

Additionally, it fixes a problem where `O_APPEND` was not working correctly
because `GENERIC_WRITE` was always being set; as a result, `FILE_WRITE_DATA`
could not be removed from the permission set to properly enable append-only
mode.

It also treats `O_TRUNC` with `O_APPEND` as an invalid argument error.  This is
because Windows cannot support these two flags together. To support `O_TRUNC`,
the `GENERIC_WRITE` bit must be set for the file access flags.  Setting this
bit will cause `FILE_WRITE_DATA` to be set, which will not properly treat the
file as append-only (it requires `FILE_APPEND_DATA` without `FILE_WRITE_DATA`).

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

@@ -67,7 +67,7 @@ hostcalls! {
     ) -> wasi::__wasi_errno_t;
 
     pub unsafe fn fd_fdstat_set_flags(
-        wasi_ctx: &WasiCtx,
+        wasi_ctx: &mut WasiCtx,
         memory: &mut [u8],
         fd: wasi::__wasi_fd_t,
         fdflags: wasi::__wasi_fdflags_t,