[LPM] Actually test what the O2 pass pipeline consists of in key places,

[LPM] Actually test what the O2 pass pipeline consists of in key places,
especially the *structure* of it with respect to various pass managers.

This uncovers an absolute horror show of problems. This test shows just
how bad PR24804 is: we have a totaly of *seven* loop pass managers in
the main optimization pipeline.

I've tried to comment the various bits to the best of my knowledge, but
more enhancements here would be great.

Also great would be folks adding various test for other pipelines, I'm
focused on trying to fix the O2 pipeline. I just wanted a test to show
what I'm changing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261305 91177308-0d34-0410-b5e6-96231b3b80d8