[Bug c++/52801] improve selective typedef unwrapping

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52801

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #2)
> (In reply to Eric Gallager from comment #1)
> > Confirmed that the notes could ease up on the template spew; g++ output is
> > now:
> 
> Note that I'm not complaining about the redundant notes listing the
> declaration of the candidates (which are the subject of a different PR that
> I cannot find right now). 
> 
> The object of improvement here is:
> 
> no known conversion from 'vector<Real>' to 'const std::basic_string<char>'
> 
> versus
>  
> no known conversion for argument 1 from ‘std::vector<double>’ to ‘const
> std::__cxx11::basic_string<char>&’
> 
> On the latter, gcc is excessively unwrapping typedef.

There's no typedef involved in those string types (well there is, as it should
show std::string, but not in either form you showed), and the presence of the &
is important.