[wasm] Avoid double-serializing the wire bytes

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 835f2f471a395159fd01f1fbb91b2c0b90345d6e..53553eb85ed505aa260c61fa34b7e8c8d4eab8e0 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -873,7 +873,8 @@ class ExternalReference BASE_EMBEDDED {
 
   ExternalReference() : address_(NULL) {}
 
-  ExternalReference(Address address, Isolate* isolate);
+  ExternalReference(Address address, Isolate* isolate,
+                    Type type = BUILTIN_CALL);
 
   ExternalReference(ApiFunction* ptr, Type type, Isolate* isolate);