[g++] Demangle the symbol of typeid.name

std::cout << typeid(*this).name() << std::endl;

check:

1. c++filt -t P3foo

2. use C++ ABI identifiers

#include <exception>
#include <iostream>
#include <cxxabi.h>
struct empty { };
template <typename T, int N>
struct bar { };
int main()
{
int     status;
char   *realname;


// exception classes not in <stdexcept>, thrown by the implementation

// instead of the user

std::bad_exception  e;

realname = abi::__cxa_demangle(e.what(), 0, 0, &status);

std::cout << e.what() << "\t=> " << realname << "\t: " << status << '\n';
  free(realname);


  // typeid
  bar<empty,17>          u;

const std::type_info  &ti = typeid(u);



realname = abi::__cxa_demangle(ti.name(), 0, 0, &status);

std::cout << ti.name() << "\t=> " << realname << "\t: " << status << '\n';



free(realname);



return 0;

}