Provide the C WASI implementation as an option.

This adds the C WASI implementation as a new crate, wasmtime-wasi-c,
and adds a command-line flag to the wasmtime command-line driver to
select which WASI implementation to use.

wasmtime-wasi-c/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name = "wasmtime-wasi-c"
+version = "0.0.0"
+authors = ["The Cranelift Project Developers"]
+publish = false
+description = "WASI API support for Wasmtime"
+categories = ["wasm"]
+repository = "https://github.com/CraneStation/wasmtime"
+license = "Apache-2.0 WITH LLVM-exception"
+readme = "README.md"
+
+[dependencies]
+wasmtime-runtime = { path = "../wasmtime-runtime" }
+wasmtime-environ = { path = "../wasmtime-environ" }
+wasmtime-jit = { path = "../wasmtime-jit" }
+cranelift-codegen = "0.30.0"
+cranelift-entity = "0.30.0"
+cranelift-wasm = "0.30.0"
+target-lexicon = "0.3.0"
+cast = { version = "0.2.2", default-features = false }
+log = { version = "0.4.6", default-features = false }
+libc = "0.2.50"
+
+[build-dependencies]
+cmake = "0.1.35"
+bindgen = "0.49.0"
+
+[badges]
+maintenance = { status = "experimental" }
+travis-ci = { repository = "CraneStation/wasmtime" }