[LV] Statistics numbers for LoopVectorize introduced: a number of analyzed…

Description

[LV] Statistics numbers for LoopVectorize introduced: a number of analyzed loops & a number of vectorized loops.
Use -stats to see how many loops were analyzed for possible vectorization and how many of them were actually vectorized.
Patch by Zinovy Nis

Differential Revision: http://reviews.llvm.org/D3438