wasi-c2: rewrite wasi-common in terms of system-interface

crates/wasi-c2/build.rs

@@ -0,0 +1,8 @@
+// Tell any dependencies, if necessary, where our WASI submodule is so they can
+// use the same witx files if they want.
+fn main() {
+    let cwd = std::env::current_dir().unwrap();
+    let wasi = cwd.join("..").join("wasi-common").join("WASI");
+    println!("cargo:wasi={}", wasi.display());
+    println!("cargo:rustc-env=WASI_ROOT={}", wasi.display());
+}