[yocto] Pyro's uninative and libstdc++ symbols

[Raphael Kubo da Costa]

I've recently updated my host system to Fedora 26, which has GCC 7.

This seems to be causing some issues on Pyro, where I have a -native
recipe that is built with my system's g++ and ends up generating a
binary with the following symbol:

    0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4.23 std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&, unsigned long, std::allocator<char> const&)

GLIBCXX_3.4.23 is not part of Pyro's uninative's libstdc++, so when that
binary is invoked in another (non-native) recipe as part of do_configure
it fails to run:

    gn: /data/src/yocto/poky/build/tmp/sysroots-uninative/x86_64-linux/usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.23' not found (required by gn)

Is there anything I should be doing differently here?