lang/gnu-apl: try to unbreak the port's build on recent -CURRENT

The base template for std::char_traits<> has been removed in LLVM 19;
specializations are only provided for char, wchar_t, char8_t, char16_t,
and char32_t. This had severely impacted GNU APL which derived its
UTF8 and UCS string classes from std::basic_string<>. The author had
made several attempts to convert these classes to use std::vector<>
instead. Carefully cherry-pick required changes so these fixes could
be applied on top of version 1.8 as trunk had diverged significantly.

Obtained from: upstream (SVN revisions 1823, 1831, and 1837)
Reported by: pkg-fallout