ICC does not define __POPCNT__
ICC does not define __POPCNT__

Contrary to what I said two commits earlier, __POPCNT__ is not defined.
According to Wikipedia, the Nehalem architecture (with SSE4.2)
introduced the popcnt instruction. Also SSE4a should contain it, though
this doesn't matter much because ICC only cares for Intel instruction
sets.
The previous implementation defined __POPCNT__ unconditionally for ICC.
Now it's only defined if __SSE4_2__ is defined.

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

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