See also: https://unicode-org.atlassian.net/browse/ICU-20530
Lots of errors of the same kind (libxml/tree.h included within extern "C"):
``
In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/8.3.0/include/g++-v8/bits/shared_ptr.h:52,
from /usr/lib/gcc/x86_64-pc-linux-gnu/8.3.0/include/g++-v8/memory:81,
from /usr/include/unicode/localpointer.h:45,
from /usr/include/unicode/uenum.h:23,
from /usr/include/unicode/ucnv.h:53,
from /usr/include/libxml2/libxml/encoding.h:31,
from /usr/include/libxml2/libxml/parser.h:810,
from /usr/include/libxml2/libxml/globals.h:18,
from /usr/include/libxml2/libxml/threads.h:35,
from /usr/include/libxml2/libxml/xmlmemory.h:218,
from /usr/include/libxml2/libxml/tree.h:1307,
from /var/tmp/portage/kde-misc/tellico-9999/work/tellico-9999/src/translators/xslthandler.h:34,
from /var/tmp/portage/kde-misc/tellico-9999/work/tellico-9999/src/translators/xsltimporter.cpp:26:
/usr/lib/gcc/x86_64-pc-linux-gnu/8.3.0/include/g++-v8/bits/shared_ptr_base.h:338:3: error: template with C linkage
template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
^~~~~~~~
``