C++ project compiled with modern compiler, but linked against outdated libstdc++

Solution 1:

Anyway, the resulting artifacts appear to be linked with system default version of libstdc++:

Yes. The devtoolset-6-gcc-c++ package provides a custom version of GCC that uses a special linker script instead of a dynamic library for libstdc++.so. That means the binaries it produces do not depend on the newer libstdc++.so.6 and can be run on other CentOS machines that don't have devtoolset installed (i.e. they only have the older libstdc++ library from GCC 4.8).

Is this build environment configuration valid?

Yes. What you're seeing is completely normal, and how it's supposed to work.

The pieces of the newer C++ runtime from GCC 6.4.0 get statically linked into your binary, and at runtime it only depends on the old libstdc++.so which every CentOS system has installed.

That's the whole point of the devtoolset version of GCC.