databases/mysql80-server: 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 databases/mysql80-client 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/databases/mysql80-client/work/mysql-8.0.39/sql/rpl_log_encryption.h:821:14:
note: in instantiation of template class 'std::basic_string<unsigned
char>' requested here
      821 |   Key_string m_encrypted_password;
          |              ^
    /usr/include/c++/v1/__fwd/string.h:23:29: note: template is declared
here
       23 | struct _LIBCPP_TEMPLATE_VIS char_traits;
          |                             ^

`Key_string` is defined as `std::basic_string<unsigned char>`, which is
no longer possible. So redefine it as a `std::vector<unsigned char>`
instead.

This requires only a few small adjustments in other places: replacing
the `length()` method with the equivalent `size()` method, and adjusting
the arguments for the `assign()` method, which for `std::vector` takes a
begin and end iterator, instead of a begin iterator and a size.

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

PR:	280693
Sponsored by:	Netzkommune GmbH

1 files changed, 19 insertions, 0 deletions

diff --git a/databases/mysql80-server/files/patch-sql_stream__cipher.h b/databases/mysql80-server/files/patch-sql_stream__cipher.h
new file mode 100644
index 000000000000..58730a516873
--- /dev/null
+++ b/databases/mysql80-server/files/patch-sql_stream__cipher.h
@@ -0,0 +1,19 @@
+--- sql/stream_cipher.h.orig	2024-07-12 19:15:25 UTC
++++ sql/stream_cipher.h
+@@ -27,6 +27,7 @@
+ #include <openssl/evp.h>
+ #include <memory>
+ #include <string>
++#include <vector>
+ 
+ /**
+   @file stream_cipher.h
+@@ -35,7 +36,7 @@
+          binary log files.
+ */
+ 
+-typedef std::basic_string<unsigned char> Key_string;
++typedef std::vector<unsigned char> Key_string;
+ 
+ /**
+   @class Stream_cipher