no-eval fallback for cwrap

cwrap returns a dynamically generated function for better performances.

However, in some environments, calling eval is not possible.
So this patch proposes a static version of cwrap when NO_DYNAMIC_EXECUTION is activated.
please add a warning here,

````
#if ASSERTIONS
    Runtime.warnOnce('using slow cwrap implementation, since NO_DYNAMIC_EXECUTION');
#endif
````