x11-wm/blackbox: 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 x11-wm/blackbox 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,
| ^
./Menu.hh:82:13: note: in instantiation of template class 'std::basic_string<unsigned int>' requested here
82 | ustring lbl;
| ^
/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 Uchar as char32_t instead of `unsigned
int` in Unicode.hh.
[1] https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals
PR: 282525
Approved by: A.J.Caines@halplant.com (maintainer)
MFH: 2024Q4
(cherry picked from commit dcc7cc48114b3730934be4236f63b5cdc0fa9821)