use WASI_ROOT env var to specify witx paths to wiggle macros

crates/wasi-common/src/wasi.rs

@@ -4,7 +4,7 @@
 use crate::WasiCtx;
 
 wiggle::from_witx!({
-    witx: ["WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx"],
+    witx: ["$WASI_ROOT/phases/snapshot/witx/wasi_snapshot_preview1.witx"],
     ctx: WasiCtx,
 });
 

crates/wasi/src/lib.rs

@@ -9,8 +9,9 @@ pub use wasi_common::{WasiCtx, WasiCtxBuilder};
 wasmtime_wiggle::wasmtime_integration!({
     // The wiggle code to integrate with lives here:
     target: wasi_common::wasi,
-    // This must be the same witx document as used above:
-    witx: ["../wasi-common/WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx"],
+    // This must be the same witx document as used above. This should be ensured by
+    // the `WASI_ROOT` env variable, which is set in wasi-common's `build.rs`.
+    witx: ["$WASI_ROOT/phases/snapshot/witx/wasi_snapshot_preview1.witx"],
     // This must be the same ctx type as used for the target:
     ctx: WasiCtx,
     // This macro will emit a struct to represent the instance,