fd_fdstat_get returns invalid fs_flags

[TerrorJack]

According to

uvwasi/src/uvwasi.c

Line 885 in 6eeddba

buf->fs_flags = r;

, fd_fdstat_get would return fs_flags directly from fcntl() call on a POSIX host. However, there's no translation logic to generate the fd flags that conform to https://github.com/WebAssembly/wasi-libc/blob/a05277a6803d99dc5f8d5c250a02cf37ff90882a/libc-bottom-half/headers/public/wasi/api.h#L896, so it's highly likely that an invalid fs_flags is passed to wasm code.