LV currently only supports power of 2 vectorization factors, which has
been made explicit with the assertion added in
840450549c9199150cbdee29acef756c19660ca1.
However, if the widest type is not a power-of-2 the computed maxVF won't
be a power-of-2 either. This patch changes getSmallestAndWidestTypes to
round up to the next power-of-2. This can happen in practice for
x86_fp80, for example. Alternatively we could force the computed max VF
to the next-lowest power-of-2
Fixes PR46139.