Exit process when proc_exit is called on Node.js WASI

because Node.js's WASI implementatin does't supprot proc_exit in async
reactor model.

See https://github.com/nodejs/node/blob/2a4452a53af65a13db4efae474162a7dcfd38dd5/lib/wasi.js#L121

Author: kateinoigakukun

Diff for: IntegrationTests/lib.js

@@ -63,7 +63,7 @@ const WASI = {
         const wasi = new NodeWASI({
             args: [programName],
             env: {},
-            returnOnExit: true,
+            returnOnExit: false,
         })
 
         return {