base64.h problems with rtorent port

Hello,

Looking for help to figure out a base64.h and tinyxml2:
https://github.com/rakshasa/rtorrent/issues/1353

Any help is welcome, thanks

```
--- rpc/xmlrpc_tinyxml2.o ---
rpc/xmlrpc_tinyxml2.cc:129:35: error: no member named 'decode_base64' in
namespace 'utils'
  129 |     return
torrent::Object(utils::decode_base64(utils::remove_newlines(child_element->ToText()->Value())));
      |                            ~~~~~~~^
rpc/xmlrpc_tinyxml2.cc:129:56: error: no member named 'remove_newlines' in
namespace 'utils'
  129 |     return
torrent::Object(utils::decode_base64(utils::remove_newlines(child_element->ToText()->Value())));
      |                                                 ~~~~~~~^
--- input/manager.o ---
3 warnings generated.
--- display/window.o ---
depbase=`echo display/window.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`; c++
-std=c++14 -DHAVE_CONFIG_H -I. -I..   -I. -I.. -isystem /usr/local/include
 -O2 -pipe -fstack-protector-strong -isystem /usr/local/include
-fno-strict-aliasing  -isystem /usr/local/include  -DNDEBUG -Wall -pthread
 -I/usr/local/include -I/usr/local/include -MT display/window.o -MD -MP -MF
$depbase.Tpo -c -o display/window.o display/window.cc && mv -f $depbase.Tpo
$depbase.Po
--- rpc/xmlrpc_tinyxml2.o ---
1 warning and 2 errors generated.
*** [rpc/xmlrpc_tinyxml2.o] Error code 1
```

-- 
Nuno Teixeira
FreeBSD UNIX:  <eduardo@FreeBSD.org>   Web:  https://FreeBSD.org