Factor out DIE lookup from lookup_function_info()
Factor out DIE lookup from lookup_function_info()

The code in lookup_function_info() is quite generic and can be used to search
for the DWARF DIEs of any external symbol (both data and functions), so move
it out to a new function which does not take an ErisFunction* and make it
return the Dwarf_Die instead.

aperezdc/eris,aperezdc/eris,aperezdc/lua-eol,aperezdc/lua-eol