[Bug libstdc++/65630] New: [5 Regression] operator+ for new std::string not exported

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65630

            Bug ID: 65630
           Summary: [5 Regression] operator+ for new std::string not
                    exported
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

#include <string>

void test01()
{
  bool test __attribute__((unused)) = true;

  std::string t;
  t = t + t;
  t = "" + t;
  t = 't' + t;
}

int main()
{
  test01();
}

This fails to link when compiled with -fno-implicit-templates

/tmp/ccKmD1iH.o: In function `test01()':
/tmp/s.cc:9: undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > std::operator+<char,
std::char_traits<char>, std::allocator<char> >(std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > const&,
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >
const&)'
/tmp/s.cc:10: undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > std::operator+<char,
std::char_traits<char>, std::allocator<char> >(char const*,
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >
const&)'
/tmp/s.cc:11: undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > std::operator+<char,
std::char_traits<char>, std::allocator<char> >(char,
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >
const&)'