cast test: test casts between different impls
cast test: test casts between different impls

in addition to simdarray and default Vc::Vector types also test
Vc::SSE::Vector and Vc::AVX::Vector types for source or destination
types (depending on the available implementations).

The test now needs way too much compile time.

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

chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,chr-engwer/Vc,VcDevel/Vc