change the runtime c code to compile with vs2015

[haskellstudio]

change typedef union Racket_Object (*Lambda)(); to typedef Racket_Object(*Lambda)(Racket_Object, Racket_Object*);

and change Racket_Object* env = malloc(sizeof(Racket_Object) * argc); to Racket_Object* env = (Racket_Object*)malloc(sizeof(Racket_Object) * argc);

then the generated code will compile success with vs2015, thank for the great tutorial