[LV] Consider Loop Unroll Hints When Making Interleave Decisions

This patch causes the loop vectorizer to not interleave loops that have
nounroll loop hints (llvm.loop.unroll.disable and llvm.loop.unroll_count(1)).
Note that if a particular interleave count is being requested
(through llvm.loop.interleave_count), it will still be honoured, regardless
of the presence of nounroll hints.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D101374