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.
Rename include dir to match the convention:
from `wasm32-wasi` to `wasm-wasi-musl`
Add building stubs which will be used to build and cache WASI
libc sysroot.
