[libcxx-commits] [libcxx] [libc++] Use __is_pointer_in_range for char_traits checks (PR #72643)

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bgra8 wrote:

heads-up @philnik777: we have about 30 test failures that have all bisected to this revision.

I noticed `std::__is_pointer_in_range()` has a deliberate UB. Replacing that with the `std::reinterpret_cast<const char*>` implementation and then rebuilding the compiler and `libc++` makes all tests pass.

Should we revert this?

https://github.com/llvm/llvm-project/pull/72643