Keep symlinks when copying build dirs of failed installations

[Flamefire]

(created using eb --new-pr)

Especially TensorFlow and PyTorch heavily use symlinks in the build folder (e.g. Bazel creates "virtual dirs" to recreate fixed folder structures).
For PyTorch this just failed for me due to recursive symlinks (couldn't check which one).

I don't see a reason to resolve symlinks which results in at least more space used and such failures as above at worst, so let's just keep the symlinks which also more closely resembles the build dir.