science/dlib-cpp: fix build with libc++ 19
As noted in the libc++ 19 release notes [1], std::char_traits<> is now
only provided for char, char8_t, char16_t, char32_t and wchar_t, and any
instantiation for other types will fail.
This causes science/dlib-cpp to fail to compile with clang 19 and libc++
19, resulting in errors similar to:
/usr/include/c++/v1/string:820:42: error: implicit instantiation of undefined template 'std::char_traits<unsigned int>'
820 | static_assert(is_same<_CharT, typename traits_type::char_type>::value,
| ^
/wrkdirs/usr/ports/science/dlib-cpp/work/dlib-19.24.6/dlib/bigint/../unicode/unicode.h:718:19: note: in instantiation of template class 'std::basic_string<unsigned int>' requested here
718 | const ustring convert_to_utf32 (
| ^
/usr/include/c++/v1/__fwd/string.h:23:29: note: template is declared here
23 | struct _LIBCPP_TEMPLATE_VIS char_traits;
| ^This can be fixed by defining unichar as char32_t instead of
uint32 in unicode.h, and adding a serializer for char32_t to
serialize.h.
[1] https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals
PR: 282665
Approved by: arrowd (maintainer)
MFH: 2024Q4