Fix build link error when change target from ios 6.0 to ios 7.0/7.1

After converting an ios project, an link error happens related to c++ std library as shown below:

"std::basic_filebuf<char, std::char_traits<char> >::is_open() const"
"std::basic_stringbuf<char, std::char_traits<char>, std::allocator<char> >::str() const"
"std::basic_ios<char, std::char_traits<char> >::widen(char) const"
"std::istream& std::istream::_M_extract<double>(double&)"

In order to fix the issue, open ios project library setting and add "libstdc++.6.0.9.dylib" to link Binary With Libraries section.