/usr/include/xbase64/xbconfig.h is in libxbase64-dev 3.1.2-6.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/xbase64/xbconfig-x86_64-linux-gnu.h
/usr/include/xbase64/xbconfig-x86_64-linux-gnu.h