detect forbidden aliasing

[Arzaghi]

Fixes #177

[Arzaghi]

As previously mentioned in the original issue(#177), there might be a lot of other candidate functions that need the same enhancement. If you confirm the current pattern, I can apply it to them as well.

[StephanTLavavej]

I resolved a merge conflict in <xutility>, where this PR was moving _Iterators_are_contiguous up, and #1527 recently added _To_pointer to that block of code. Now I just realized that I probably should have built and minimally tested the code before pushing, since _To_pointer might have depended on code in the middle, but we'll see if this works 😹

[strega-nil-ms]

I've pushed a cleanup and merge commit; this squashes the existing work, since the last "real" commit was from two years ago.

[StephanTLavavej]

There are numerous test failures that need to be investigated.

[StephanTLavavej]

Thanks! (And apologies for taking 2 years to review this! 🙀 And thanks @strega-nil-ms for cleaning up the accumulated merge conflicts! 😻) I've pushed some changes, including a major expansion of test coverage:

• Add preprocessor comment.
• <xutility> doesn't need to include <cstdio>.
• Early return within if constexpr.
  • This diff looks horrible until you ignore whitespace.
• Move call from _Swap_ranges_unchecked to swap_ranges.
• Drop commented-out code in _Copy_unchecked.
• Drop unused 4-arg overload.
• Add positive test coverage.
• Add negative test coverage.

I explored applying the 4-arg overload to ranges::swap_ranges but that would need more work (non-copyable input iterators failed to compile), so for now only the classic std::swap_ranges is enhanced.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks again for improving these debugging checks! 🐞 🚀 🎉