Comment # 5 on bug 1025863 from Michal Srb

I now have a working patch that lets you select the preferred gcc version (and
from that the libstdc++ version) at built time and lets you override the
selection with parameter at run time.

However, I am unsure if it is a good idea to set it during build. What worries
me is that in Leap 42.3 the package transitively Required by clang is
libstdc++48-devel. That is quite old version and does not support many modern
C++ features that clang supports.

There may be users that have libstdc++ 6 or 7 installed and use it with clang
and it just works. If we change clang to select libstdc++ 4.8 by default,
things may break. And the only way to make them work again would be by using
the runtime option that nobody knows.

I am currently leaning to add the patch, but to not set any default, so clang
will keep selecting the newest gcc. In addition I will check if we could add
some warning like "The selected gcc version (7) does not seem to have matching
libstdc++ installed. You may need to install it or use --gcc-preferred-version
parameter to select another version."