devel/llvm13: fix build with clang 19

Clang 19 now implements CWG 96 [1], which requires a template argument
list after a 'template' keyword, resulting in errors similar to:

 
/wrkdirs/usr/ports/devel/llvm13/work/llvm-project-13.0.1.src/flang/include/flang/Evaluate/integer.h:310:32:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    310 |       auto back{FROM::template ConvertSigned(result.value)};
        |                                ^

Upstream has committed a fix to their main branch [2], but it does not
apply cleanly to 13.0.1, so add a backported patch.

[1] https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#96
[2]
https://github.com/llvm/llvm-project/commit/7bc7672925f8154be3b8220365d3f269ac43621c

PR:		281486
Approved by:	brooks (maintainer)
MFH:		2024Q3

(cherry picked from commit e34a77083e96050812b4f082efc716dd16069c82)

devel/llvm13: 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 devel/llvm13 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 char>'
      820 |   static_assert(is_same<_CharT, typename
traits_type::char_type>::value,
          |                                          ^
   
/wrkdirs/usr/ports/devel/llvm13/work-default/llvm-project-13.0.1.src/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp:595:34:
note: in instantiation of template class 'std::basic_string<unsigned char>'
requested here
      638 |       std::basic_string<uint8_t> zeros(reg_info.byte_size, '\0');
          |                                  ^