Begin collecting some of the statistics for block placement discussed on

Begin collecting some of the statistics for block placement discussed on
the mailing list. Suggestions for other statistics to collect would be
awesome. =]

Currently these are implemented as a separate pass guarded by a separate
flag. I'm not thrilled by that, but I wanted to be able to collect the
statistics for the old code placement as well as the new in order to
have a point of comparison. I'm planning on folding them into the single
pass if / when there is only one pass of interest.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143537 91177308-0d34-0410-b5e6-96231b3b80d8