Qt 5 cross building: what is done right now
===========================================

general / cmake buildsystem:
 - Qt binaries are moved into non-multiarch location /usr/lib/qt5/bin,
   symlinks for the old location are provided for compatibility
 - All packages containing binaries are now M-A:foreign
 - Some packages (qt3d, qtwayland) had binaries split to allow that
 - qtchooser is updated to use the new binaries path
 - qttools5-dev-tools now depends on libqt5sql5-sqlite (not uploaded yet)

qmake buildsystem:
 - qmake is split into qt5-qmake-bin (M-A:foreign) and qt5-qmake (M-A:same)
 - debhelper now generates a qt.conf file with host paths and passes it to qmake
 - debhelper now passes cross QMAKE_CC, QMAKE_CXX to qmake when needed

autotools buildsystem:
 - qt5-qmake now ships /usr/bin/$(DEB_HOST_GNU_TYPE)-qmake executable for use
   with AC_CHECK_TOOL (not uploaded yet)

TODO items:
 - Make it possible to cross build Qt's own packages: drop custom configure
   code in favour of debhelper's, fix other issues
 - Check multi-arch hinter output? (https://wiki.debian.org/MultiArch/Hints)