Rewrite operator return type deduction
Rewrite operator return type deduction

This fixes a failure on `int_v x long`, which should be ill-formed but
wasn't (because long is convertible to int_v). Now long still is
convertible to int_v (else I'd break source compatibility to 1.3), but
the combination isn't allowed on binary operators (as was the case in
1.3).

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc