Fixes for cargo publish (#1416)

* Publishing fixes.

* Make WASI a symlink.

* More fixes.

* Cargo doesn't allow dev-dependencies to have optional features.

* Remove the symlink.

* Add WASI as another git submodule.

crates/wasi-common/Cargo.toml

@@ -9,6 +9,7 @@ keywords = ["webassembly", "wasm"]
 repository = "https://github.com/bytecodealliance/wasmtime"
 readme = "README.md"
 edition = "2018"
+include = ["src/**/*", "LICENSE", "WASI/phases"]
 
 [dependencies]
 anyhow = "1.0"