Investigate special linker script instead of a dynamic library for libstdc++.so

Currently, we recommend applications to be built on the oldest still-supported LTS release of Ubuntu. However, some applications need newer C++ compilers, which means that developers usually pull in a PPA that results in binaries being compiled in a way such that they don't work with the original libstdc++ that originally came with the oldest still-supported LTS release of Ubuntu.

Apparently CentOS devtoolset offers a solution for this issue.

We should understand how this magic in CentOS devtoolset works, and how it can be used with Ubuntu LTS...

https://stackoverflow.com/questions/52609269/c-project-compiled-with-modern-compiler-but-linked-against-outdated-libstdc/52611144#52611144

> 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).

We should then document it in docs.appimage.org...

Reference:
https://github.com/wheybags/glibc_version_header/issues/20

cc @TheAssassin