WinRT qmake: use "clean" makefiles for all host builds. Squash w/ 89745000

We host build all WinRT mkspecs, so go ahead and use WinCE-style makefiles
for all targets.

Change-Id: I7a85f13ec0c2c03b5cb02f94d97f16f53400e60f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>