[clang] [clang] LazyOffsetPtr: Use native pointer width (PR #111995)

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ernsteiswuerfel wrote:

This also fixes issue [#86460](https://github.com/llvm/llvm-project/issues/86460)!

The patch applies cleanly on top of 19.1.2 (tested on ppc32-musl).

https://github.com/llvm/llvm-project/pull/111995