added specialization for void return trampoline

test output:

    Hello, World!
    Hello, World!
    Hello, World!	Cat Dog	9001	function: 0x7f55f5f44300	true
    10	5
    sum is 12.200000 10.000000
    void_add(hello, 1000.000000)!!!!!
    int_add(hello, 1000.000000)!!!!!

I also verified using `__PRETTY_FUNCTION__` that the correct specialization is indeed being called.