Remove empty.h from CLEANFILES, so that after mkfiles.pl has

[u/mdw/putty] / windows / website.url

[InternetShortcut]
URL=http://www.chiark.greenend.org.uk/~sgtatham/putty/
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0