Sometimes substitution of basic_string by one of the std::string 
typeedef fails. Here is the fix.

     libstdc++: Fix gdb pretty printers when dealing with std::string

     Since revision 33b43b0d8cd2de722d177ef823930500948a7487 std::string 
and other
     similar typedef are ambiguous from a gdb point of view because it 
matches both
     std::basic_string<char> and std::__cxx11::basic_string<char> 
symbols. For those
     typedef add a workaround to accept the substitution as long as the 
same regardless
     of __cxx11 namespace.

     Also avoid to register printers for types in std::__cxx11::__8:: 
namespace, there is
     no such symbols.

     libstdc++-v3/ChangeLog:

             * libstdc++-v3/python/libstdcxx/v6/printers.py 
(Printer.add_version): Do not add
             version namespace for __cxx11 symbols.
             (add_one_template_type_printer): Likewise.
             (add_one_type_printer): Likewise.
             (FilteringTypePrinter._recognizer.recognize): Add a 
workaround for std::string & al
             ambiguous typedef matching both std:: and std::__cxx11:: 
symbols.
             (register_type_printers): Refine type registration to limit 
false positive in
             FilteringTypePrinter._recognize.recognize requiring to look 
for the type in gdb.
             * libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx17.cc: 
Remove obsolete
             \#define _GLIBCXX_USE_CXX11_ABI 0.
             * 
libstdc++-v3/testsuite/libstdc++-prettyprinters/simple.cc: Likewise.
             * 
libstdc++-v3/testsuite/libstdc++-prettyprinters/simple11.cc: Likewise.
             * 
libstdc++-v3/testsuite/libstdc++-prettyprinters/whatis.cc: Likewise.
             * libstdc++-v3/testsuite/libstdc++-prettyprinters/80276.cc: 
Likewise and remove
             xfail for c++20 and debug mode.
             * 
libstdc++-v3/testsuite/libstdc++-prettyprinters/libfundts.cc: Likewise.

Tested under x86_64 linux w/o _GLIBCXX_INLINE_VERSION and w/o 
_GLIBCXX_DEBUG.

I also tested it with my patch to use cxx11 abi in 
_GLIBCXX_INLINE_VERSION mode.

Ok to commit ?

François