Do much the same for libstdc++ as we do for libgfortran on Linux

[staticfloat]

This distributes the system libstdc++.so.X alongside Julia when you make dist.

@tkelman

[tkelman]

Background for anyone who wasn't following along in #8442 - the devtoolset gcc we had been using on the centos 5 buildbots to create generic linux binary tarballs (used on Travis for language: julia, and convenient on distributions that don't have Julia packaged, or for testing nightlies) does some strange packaging of libgfortran and libstdc++. We were accidentally including a libgfortran from centos 5's system gcc 4.1.2 in the binaries, which breaks a lot of packages that have Fortran dependencies. (It's a little surprising that base Julia's Fortran dependencies were working at all.)

So we need to build our own gcc on the buildbots, which is now done, and also bundle libstdc++ (this pr).

If someone were to use clang or libc++, I think this would be a no-op, right? And I don't think distribution packagers are using make dist so this doesn't change anything there.

[staticfloat]

Yep. The script will probably print something nebulous out like "basename: argument required", but if it fails, things just continue on their merry way.

[ViralBShah]

Bundling libstdc++ is much needed! Thanks.

[tkelman]

backported in d97b3ba