* Auto-generate shims for old `wasi_unstable` module
This commit is effectively just doing what #707 already did, but
applying it to the `snapshot_0` module as well. The end result is the
same, where we cut down on all the boilerplate in `snapshot_0` and bring
it in line with the main `wasi_snapshot_preview1` implementation. The
goal here is to make it easier to change the two in tandem since they're
both doing the same thing.
* Migrate `wasi_common::hostcalls` to a macro
This commit migrates the `hostcalls` module to being auto-generated by a
macro rather than duplicating a handwritten signature for each wasi
syscall.
* Auto-generate snapshot_0's `hostcalls` module
Similar to the previous commit, but for `snapshot_0`
* Delete the `wasi-common-cbindgen` crate
This is no longer needed with the hostcalls macro now, we can easily
fold the definition of the cbindgen macro into the same crate.
* Rustfmt
* Fix windows build errors
* Rustfmt
* Remove now no-longer-necessary code
* rustfmt
5953215bac