[clang] [compiler-rt] [llvm] [ConstantFolding] Canonicalize constexpr GEPs to i8 (PR #89872)

[Arthur Eubanks via cfe-commits]

https://github.com/aeubanks approved this pull request.

we've resolved the performance regression from the previous patch internally, thanks for waiting!

https://github.com/llvm/llvm-project/pull/89872