[wasm] Support asm.js modules with a single function.

test/mjsunit/wasm/asm-wasm.js

Index: test/mjsunit/wasm/asm-wasm.js
diff --git a/test/mjsunit/wasm/asm-wasm.js b/test/mjsunit/wasm/asm-wasm.js
index a580c5c7e94a2f0ef804c6477857e9333aaa86f2..f316e6837f7273533f93393bde0d525b7c537ee8 100644
--- a/test/mjsunit/wasm/asm-wasm.js
+++ b/test/mjsunit/wasm/asm-wasm.js
@@ -1581,3 +1581,16 @@ function TestLoopsWithUnsigned() {
 }
 
 assertWasm(323, TestLoopsWithUnsigned);
+
+
+function TestSingleFunctionModule() {
+  "use asm";
+  function add(a, b) {
+    a = a | 0;
+    b = b | 0;
+    return (a + b) | 0;
+  }
+  return add;
+}
+
+assertEquals(7, TestSingleFunctionModule()(3, 4));