qt5: make sure this file is never accidentally used
Fix OS/2 builds. I have no idea why.
mimetypes: use a correct xml file, not some gitorious' HTML wrapper
os2: use a rudimentary, mock "implementation" of QStandardDirs

It looks like the code shall fall back to the bundled XML file, so let's just
return empty QStringList and be done with it. Shall fix the link error at least.