Save sizes of built dynamic libraries and sys images

[Zentrik]

I just picked some big files that seemed related to Julia or LLVM.
The results are not shown in the report currently, I don't expect these sizes to change much frequently so it didn't seem necessary. I plan on adding these to https://tealquaternion.camdvr.org/.
I've tried to make sure even if fetching/ saving the sizes fails it doesn't affect anything else.

I wasn't sure how to test this locally.

[maleadt]

LGTM, but @vtjnash would have to deploy this to the benchmark cluster (i.e. #125).

[vtjnash]

I should try to see if anyone else has an MIT account who can also update the server, as I don't have too much time to deal with updates often. Otherwise though, this seems like a good idea. I had sometimes been scraping the buildkite logs for this same purpose, but I don't know if that runs the make build-stats steps anymore which would be a necessary prerequisite for it

[Zentrik]

I think once JuliaLang/julia#53902 is merged, JuliaCI/julia-buildkite#224 can be merged to reenable build-stats at which point this pr isn't particularly useful.