qt5: Use the old "builddir hack" for Qt5's own QMake-using modules.

Many work (e.g. qtxmlpatterns) work just fine with qmake using srcdir !=
builddir, but most do not and instead assume a srcdir == builddir.

This is difficult for kdesrc-build (we generally assume we can delete
everything under the build directory) so reintroduce the old builddir
hack that symlinks all the files in the srcdir under the builddir.

To avoid needlessly throwing symlinks around for the existing
QMake-using modules (which apparently all already work), this only
applies to modules with a repository under qt.io.

Note that qtbase should be handled by a separate build system (still
called "Qt4.pm" and doesn't fall under this hack.