Problem when compile about std::string by ESP8266-DEVKIT's GCC-xtensa version 5.2.0.

[TridentTD]

When I build code like as the following by ESP8266-DEVKIT's GCC-xtensa version 5.2.0.

#include <string>

....

  const char *arr  = "HelloArray";
  std::string str = arr;
...

I found some error

(.text.setup+0x14): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_S_copy_chars(char*, char const*, char const*)'
(.text.setup+0x18): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_dispose()'
undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_S_copy_chars(char*, char const*, char const*)'
In function `void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char const*>(char const*, char const*, std::forward_iterator_tag)':
xtensa-lx106-elf\include\c++\5.2.0\bits/basic_string.tcc:229: undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_dispose()'

collect2.exe: error: ld returned 1 exit status

And this version gcc-xtensa 5.2.0 std::to_string missing ? Do you mind to upgrade to other version of gcc-xtensa for esp-devkit.

Thank you.