Too many libstdc++ in the distributed tarball

[giordano]

% wget -qO - 'https://julialangnightlies-s3.julialang.org/bin/linux/x64/julia-latest-linux64.tar.gz' | tar tzvf - | grep "libstdc++"
-rwxr-xr-x buildworker/buildworker  11509696 2020-12-07 20:31 julia-18b7fee975/lib/julia/libstdc++.so.6.0.23
-rwxr-xr-x buildworker/buildworker  22521088 2020-12-07 20:31 julia-18b7fee975/lib/julia/libstdc++.so.6.0.26
lrwxrwxrwx buildworker/buildworker         0 2020-12-07 20:31 julia-18b7fee975/lib/julia/libstdc++.so.6 -> libstdc++.so.6.0.26

The tarball contains two different libstdc++, probably the old one is a remnant of #38347