NEON: make common code usable for non-SSE targets

Signed-off-by: Matthias Kretz <kretz@kde.org>
NEON: clean up boilerplate to get it compiling

Added the necessary headers to get NEON code to compile initially. The
load.cpp checkAlignment test compiles and passes with this.

Signed-off-by: Matthias Kretz <kretz@kde.org>
unittest: less explicit Vector<T> instantiation

the ULP code lead to the requirement of abs/frexp/ldexp and more to be
implemented before any unit test was compilable. That is not usable for
implementing a new target. This can be fixed by having the functions
only instantiated when used (via templates). There may still be a small
error here, but at least NEON stuff can be compiled now.

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