Add a flag to defer vectorization into a phase after the inliner and its

Add a flag to defer vectorization into a phase after the inliner and its
CGSCC pass manager. This should insulate the inlining decisions from the
vectorization decisions, however it may have both compile time and code
size problems so it is just an experimental option right now.

Adding this based on a discussion with Arnold and it seems at least
worth having this flag for us to both run some experiments to see if
this strategy is workable. It may solve some of the regressions seen
with the loop vectorizer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184698 91177308-0d34-0410-b5e6-96231b3b80d8