[LoopVectorize] Factor out duplicated code into Report::emitAnalysis

The logic in emitAnalysis is duplicated across multiple functions.  This
splits it into a function.  Another use will be added by the patchset.

NFC.  This is part of the patchset that splits out the memory dependence logic
from LoopVectorizationLegality into a new class LoopAccessAnalysis.
LoopAccessAnalysis will be used by the new Loop Distribution pass.

llvm-svn: 227748