Add optimization remarks to the loop unroller and vectorizer.

Summary:
This calls emitOptimizationRemark from the loop unroller and vectorizer
at the point where they make a positive transformation. For the
vectorizer, it reports vectorization and interleave factors. For the
loop unroller, it reports all the different supported types of
unrolling.

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3456