test interleaving scatter: generic implementation
test interleaving scatter: generic implementation

Use index_sequences to generically implement the test. This gets rid of
the ugly macro hacks and also tests the assignment to std::array.

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

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