Write out the copy ctor for clang < 3.7
Write out the copy ctor for clang < 3.7

Clang < 3.7 miscompiles the defaulted copy constructor of Adapter. By
explicitly writing out the call to the Base constructor the failure goes
away.

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

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