[captaincrutches]

LLVM 23 made some breaking cleanups of transitive includes in libc++, which aligns system headers more closely with the spec but does in fact break a few xenium headers.

3 fixes for 3 files here. Reproducible with for file in $(ls xenium/*.hpp); do clang++ -c -I. -stdlib=libc++ $file; done

xenium/hash.hpp:47:37: error: no member named 'alignment_of' in namespace 'std'
   47 |     constexpr auto alignment = std::alignment_of<Key>();
      |                                     ^~~~~~~~~~~~

alignment_of is defined in type_traits, so added that.

xenium/policy.hpp:60:16: error: no type named 'size_t' in namespace 'std'
   60 | template <std::size_t Value>
      |           ~~~~~^

policy.hpp includes cstdint, but size_t is actually defined in cstddef (among others), so changed that.

xenium/aligned_object.hpp:34:25: error: no type named 'align_val_t' in namespace 'std'
   34 |   static constexpr std::align_val_t alignment() {
      |                    ~~~~~^

align_val_t is defined in new, so added that.

It all still compiles with all the compilers I happen to have installed: gcc-16, clang-22, and clang-23 (both libc++ and libstdc++).

[captaincrutches]

Rebased onto dev to fix the conflicts after the target change.

(The cmake changes there are most welcome, and work great when I point my consuming project at dev, so thanks for that too! 🎉)