Enable the vectorizer to access interleaved memory. This means that,
when it's decided to be profitable, the memory accesses can be
vectorized instead of the value being built up by a sequence of
load_lane instructions. This will often increase the vectorization
factor of the loop, leading to significantly better performance.

I run a reasonably large collection of benchmarks and most are not
affected by this change, with most performance changes <1%. But I see a
2.5% speedup for the total run time of TSVC, 1% speedup for SPEC2017
x265, 28% speedup for a ResNet workload and 95% for libyuv. This is
running V8 on an AArch64 box.