[clang] [NFC] Remove unnecessary copy of Triple in ItaniumMangle.cpp (PR #102469)

[Nikita Popov via cfe-commits]

nikic wrote:

Could you please also adjust the other use in https://github.com/llvm/llvm-project/pull/101696/files#diff-e0ad0cd86168ae6b1bdbc14d96dce7bd4de45ec1da69b9ac18dacb7adf1e453cR7060?

https://github.com/llvm/llvm-project/pull/102469