[v3] define string::pop_back()

[Eric Botcazou]

>         * include/bits/basic_string.h (basic_string::at): Move adjacent to
> other overload.
>         (basic_string::pop_back): Define.
>         * include/debug/string (__gnu_debug::basic_string::pop_back):
> Likewise. * include/ext/vstring.h (__versa_string::pop_back): Likewise. *
> config/abi/pre/gnu.ver: Add new symbols.
>         * testsuite/21_strings/basic_string/modifiers/char/pop_back.cc:
> New. * testsuite/21_strings/basic_string/modifiers/wchar_t/pop_back.cc:
> New. * testsuite/21_strings/basic_string/range_access.cc: Split to ... *
> testsuite/21_strings/basic_string/range_access/char/1.cc: Here and ... *
> testsuite/21_strings/basic_string/range_access/wchar_t/1.cc: Here. *
> testsuite/ext/vstring/modifiers/char/pop_back.cc: New.
>         * testsuite/ext/vstring/modifiers/wchar_t/pop_back.cc: New.

This breaks bootstrap on Solaris:

ld: fatal: libstdc++-symbols.ver-sun: 4806: symbol `std::basic_string<char, 
std::char_traits<char>, std::allocator<char> >::pop_back()' is already defined 
in file: libstdc++-symbols.ver-sun

_ZNSs8pop_backEv is referenced twice in the version file.

-- 
Eric Botcazou