[PM] Don't require analysis results to be const in the new pass manager.

I think this was just over-eagerness on my part. The analysis results
need to often be non-const because they need to (in some cases at least)
be updated by the transformation pass in order to remain correct. It
also makes lazy analyses (a common case) needlessly annoying to write in
order to make their entire state mutable.

llvm-svn: 200881