Fix clang build + misc fixes
Seeing this in FreeBSD CI jobs:
/builds/bobsayshilol/calligra/filters/words/msword-odf/wv2/src/utilities.h:29:51: error: no template named 'unary_function' in namespace 'std'; did you mean '__unary_function'?
29 | template<class T> struct Delete : public std::unary_function<T*, void>
| ~~~~~^~~~~~~~~~~~~~
| __unary_function[ 19%] Building CXX object filters/words/msword-odf/wv2/src/CMakeFiles/kowv2.dir/word95_helper.cpp.o
This MR fixes that as well as some other warnings when trying to build with clang.