[clang] [Clang] Add -fwrapv-pointer flag (PR #122486)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

CC @llvm/clang-vendors : this changes the behavior of -fwrapv.

Internally, I expect it's going to be a bit painful to communicate to all our internal teams that they need to change their -fwrapv usage to -fno-strict-overflow, but if we think it's important to align with gcc in that respect, we can do it, I guess?

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The implementation looks correct.

https://github.com/llvm/llvm-project/pull/122486