Fix -mfpmath usage after breaking it yesterday
Fix -mfpmath usage after breaking it yesterday

The scalar unit tests require at least SSE2 to enable -mfpmath=sse so
that we get reproducible results on FP.

While at it, I cleaned up the logic for setting up the flags for the
different targets.

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

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