qt5-static: Fixes for cmake

This time for real. -static is passed in as INTERFACE_LINK_LIBRARIES
because nothing else works, and this is the sort of thing that cmake
considers acceptable practice:

http://www.cmake.org/cmake/help/v3.0/command/target_link_libraries.html

"Specify libraries or flags to use when linking a given target"

.. because what's in a name after all? flags/libraries, tomato/tomato.