qt: Force arm mode instead of Thumb1 mode

Qt has some assembly that doesn't exist in thumb1 mode.
So, force arm mode for Qt

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>