[NFC] Fix comments in PassBuilder functions (#89513)

The original comments mention `addPreLinkLTODefaultPipeline`, but I
could not find any functions with this name, even in
https://reviews.llvm.org/D33540
(8b3be4e5) where this comment was added.
I assume they meant to refer to `buildThinLTOPreLinkDefaultPipeline` and
`buildLTOPreLinkDefaultPipeline` and so this patch uses them.