MSVC: Fix compile and different approach for ignore dead store
MSVC: Fix compile and different approach for ignore dead store

This requires a conversion operator to long long for 64-bit argument
usage.

Also `x = x` was not good enough for MSVC as an alternative to `asm(""
::"m"(x))`.

Refs: gh-119
Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

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