ulp: make ulpDiffToReferenceSigned callable with any type
ulp: make ulpDiffToReferenceSigned callable with any type

ulpDiffToReferenceSigned calls are useful for floating-point types only.
But to make it more convenient to use in a generic function allow all
other types as well and just return 0.

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

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