[llvm] [LTO] Reset DiscardValueNames in optimize(). (PR #78705)

[Steven Wu via llvm-commits]

https://github.com/cachemeifyoucan commented:

I think the flag doesn't work because `.bc` is `save-temp` outputs that are not real outputs from libLTO but only for debugging intermediates. I am not against the quality of life improvement here.

Is this a FullLTO problem only or it affects thinLTO as well? 

https://github.com/llvm/llvm-project/pull/78705