wasm2js: get rid of some non-flat code assumptions (#2036)

We run flatten there, which lets us simplify things a lot. Turns out that for assertions we didn't run it, which is why we still needed the old non-flat code paths. This adds flatten there and removes that old code and assumptions.

Author: kripken

src/tools/wasm2js.cpp

@@ -57,6 +57,7 @@ class AssertionEmitter {
   SExpressionWasmBuilder& sexpBuilder;
   Output& out;
   Wasm2JSBuilder::Flags flags;
+  Module tempAllocationModule;
 
   Ref emitAssertReturnFunc(Builder& wasmBuilder,
                            Element& e,
@@ -75,7 +76,7 @@ class AssertionEmitter {
 
   Ref processFunction(Function* func) {
     Wasm2JSBuilder sub(flags);
-    return sub.processFunction(nullptr, func);
+    return sub.processStandaloneFunction(&tempAllocationModule, func);
   }
 
   void emitFunction(Ref func) {