* If a function prototype is declarated inside a function, do not
  translate it to a top-level extern function declaration. Similar to
  extern local variable, just wrapped it into a block-local struct.

* Add a new extern_local_fn tag of aro_translate_c node for present
  extern local function declaration.

* When a function body has a C function prototype declaration, it adds
  an extern local function declaration. Subsequent function references
  will look for this function declaration.