Find our JIT'ed function and run it

Here is where the magic happens. We first mangle the symbol before
passing it to findSymbolIn: The compilation then happens here. It will
spit back a FFI pointer, which we then need to invoke ourselves.

In order to do this we have to specify the Haskell type of the function
that we're pointing to, which resides in C-land, hence the ccall
attribute in our foreign declaration.

Try it out!