Some notable changes:
- `ENOENT` is returned instead of `ENOTCAPABLE` when a path has not
be pre-opened (https://github.com/WebAssembly/wasi-libc/pull/370)
- `fd_readdir()`: some implementations may not set the inode number,
so an additional call to `fstatat()` is now done in order to get it
when that happens.
* Update wasi-libc to a00bf321eeeca836ee2a0d2d25aeb8524107b8cc
It includes a port of emscripten's allocator that performs
performs much better than the old one.
Most importantly, it includes the prerequisites to later add
support for POSIX threads.
