cad/kicad: 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 cad/kicad to fail to compile with clang 19 and libc++ 19,
resulting in errors similar to:

  /wrkdirs/usr/ports/cad/kicad/work/kicad-7.0.2/thirdparty/nanodbc/nanodbc/nanodbc.cpp:261:25: error: implicit instantiation of undefined template 'std::char_traits<unsigned short>'
    261 |     auto const n = std::char_traits<NANODBC_SQLCHAR>::length(array);
        |                         ^
  /usr/include/c++/v1/__string/char_traits.h:45:8: note: template is declared here
     45 | struct char_traits;
        |        ^
  /wrkdirs/usr/ports/cad/kicad/work/kicad-7.0.2/thirdparty/nanodbc/nanodbc/nanodbc.cpp:3576:52: error: implicit instantiation of undefined template 'std::char_traits<unsigned short>'
   3576 |             dsn.name = string(&name[0], &name[std::char_traits<NANODBC_SQLCHAR>::length(name)]);
        |                                                    ^
  /usr/include/c++/v1/__string/char_traits.h:45:8: note: template is declared here
     45 | struct char_traits;
        |        ^
  /wrkdirs/usr/ports/cad/kicad/work/kicad-7.0.2/thirdparty/nanodbc/nanodbc/nanodbc.cpp:3578:49: error: implicit instantiation of undefined template 'std::char_traits<unsigned short>'
   3578 |                 string(&driver[0], &driver[std::char_traits<NANODBC_SQLCHAR>::length(driver)]);
        |                                                 ^
  /usr/include/c++/v1/__string/char_traits.h:45:8: note: template is declared here
     45 | struct char_traits;
        |        ^
  /wrkdirs/usr/ports/cad/kicad/work/kicad-7.0.2/thirdparty/nanodbc/nanodbc/nanodbc.cpp:3629:54: error: implicit instantiation of undefined template 'std::char_traits<unsigned short>'
   3629 |             drv.name = string(&descr[0], &descr[std::char_traits<NANODBC_SQLCHAR>::length(descr)]);
        |                                                      ^
  /usr/include/c++/v1/__string/char_traits.h:45:8: note: template is declared here
     45 | struct char_traits;
        |        ^

and:

  /usr/include/c++/v1/string:820:42: error: implicit instantiation of undefined template 'std::char_traits<unsigned short>'
    820 |   static_assert(is_same<_CharT, typename traits_type::char_type>::value,
        |                                          ^
  /wrkdirs/usr/ports/cad/kicad/work/kicad-7.0.2/thirdparty/compoundfilereader/compoundfilereader.h:226:21: note: in instantiation of template class 'std::basic_string<unsigned short>' requested here
    226 |         utf16string dir;
        |                     ^
  /usr/include/c++/v1/__fwd/string.h:23:29: note: template is declared here
     23 | struct _LIBCPP_TEMPLATE_VIS char_traits;
        |                             ^

The first batch of errors can be fixed by providing a simple `length()`
function for the `NANODBC_SQLCHAR const*` type. The second batch can be
fixed by using `std::basic_string<char16_t>` for `utf16string`, and
adjusting the call to `std::basic_string<char16_t>::append`.

[1] https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals

PR:             281886
MFH:            2024Q3

2 files changed, 64 insertions, 0 deletions

diff --git a/cad/kicad/files/patch-thirdparty_compoundfilereader_compoundfilereader.h b/cad/kicad/files/patch-thirdparty_compoundfilereader_compoundfilereader.h
new file mode 100644
index 000000000000..e076a7d505d2
--- /dev/null
+++ b/cad/kicad/files/patch-thirdparty_compoundfilereader_compoundfilereader.h
@@ -0,0 +1,20 @@
+--- thirdparty/compoundfilereader/compoundfilereader.h.orig	2023-04-13 20:27:39 UTC
++++ thirdparty/compoundfilereader/compoundfilereader.h
+@@ -129,7 +129,7 @@ struct helper
+     }
+ };
+ 
+-typedef std::basic_string<uint16_t> utf16string;
++typedef std::basic_string<char16_t> utf16string;
+ typedef std::function<void(const COMPOUND_FILE_ENTRY*, const utf16string& dir, int level)> 
+     EnumFilesCallback;
+ 
+@@ -246,7 +246,7 @@ class CompoundFileReader (private)
+             utf16string newDir = dir;
+             if (dir.length() != 0)
+                 newDir.append(1, '\n');
+-            newDir.append(entry->name, entry->nameLen / 2);
++            newDir.append(reinterpret_cast<const char16_t*>(entry->name), entry->nameLen / 2);
+             EnumNodes(GetEntry(entry->childID), currentLevel + 1, maxLevel, newDir, callback);
+         }
+ 
diff --git a/cad/kicad/files/patch-thirdparty_nanodbc_nanodbc_nanodbc.cpp b/cad/kicad/files/patch-thirdparty_nanodbc_nanodbc_nanodbc.cpp
new file mode 100644
index 000000000000..685a94fc55c7
--- /dev/null
+++ b/cad/kicad/files/patch-thirdparty_nanodbc_nanodbc_nanodbc.cpp
@@ -0,0 +1,44 @@
+--- thirdparty/nanodbc/nanodbc/nanodbc.cpp.orig	2023-04-13 20:27:39 UTC
++++ thirdparty/nanodbc/nanodbc/nanodbc.cpp
+@@ -255,10 +255,19 @@ constexpr std::size_t size(const T (&array)[N]) noexce
+ }
+ #endif
+ 
++inline std::size_t length(NANODBC_SQLCHAR const* s)
++{
++  std::size_t len = 0;
++  for (; *s != 0; ++s)
++    ++len;
++  return len;
++  
++}
++
+ template <std::size_t N>
+ inline std::size_t size(NANODBC_SQLCHAR const (&array)[N]) noexcept
+ {
+-    auto const n = std::char_traits<NANODBC_SQLCHAR>::length(array);
++    auto const n = length(array);
+     NANODBC_ASSERT(n < N);
+     return n < N ? n : N - 1;
+ }
+@@ -3573,9 +3582,9 @@ std::list<datasource> list_datasources()
+                 "incompatible SQLCHAR and string::value_type");
+ 
+             datasource dsn;
+-            dsn.name = string(&name[0], &name[std::char_traits<NANODBC_SQLCHAR>::length(name)]);
++            dsn.name = string(&name[0], &name[length(name)]);
+             dsn.driver =
+-                string(&driver[0], &driver[std::char_traits<NANODBC_SQLCHAR>::length(driver)]);
++                string(&driver[0], &driver[length(driver)]);
+ 
+             dsns.push_back(std::move(dsn));
+             direction = SQL_FETCH_NEXT;
+@@ -3626,7 +3635,7 @@ std::list<driver> list_drivers()
+                 "incompatible SQLCHAR and string::value_type");
+ 
+             driver drv;
+-            drv.name = string(&descr[0], &descr[std::char_traits<NANODBC_SQLCHAR>::length(descr)]);
++            drv.name = string(&descr[0], &descr[length(descr)]);
+ 
+             // Split "Key1=Value1\0Key2=Value2\0\0" into list of key-value pairs
+             auto beg = &attrs[0];