Currently when we have a member function that has an auto return type and the definition is out of line we generate two DWARF DIE.
One for the declaration and a second one for the definition. We don't currently lookup the definition in order to replace the auto return type with a real one.
This modifies DWARFASTParserClang to detect we have a function with deduced return type and lookup the
definition to obtain the correct return type and adjust the FunctionDecl to reflect this.
What's the purpose of this? Do we expect to see the type attribute more than once?