O_RESOLVE_BENEATH is forced

[yamt]

in posix, openat(dirfd, "../b", ...) should work. however, in wasi, O_RESOLVE_BENEATH behavior is unconditionally applied. (at least in popular implementations. i don't know if it was well documented for preview1. but for later versions, see https://github.com/WebAssembly/wasi-filesystem/blob/main/path-resolution.md.) wasi-ilbc doesn't seem to emulate the posix behavior either.