[llvm] [BOLT][DWARF][NFC] Change how we re-size CloneUnitCtxMap (PR #75876)

[Amir Ayupov via llvm-commits]

https://github.com/aaupov commented:

Please retitle to avoid "we" and update the summary to provide more context to the readers with no background.

https://github.com/llvm/llvm-project/pull/75876