Rename class 'CFGReachabilityAnalysis' to 'CFGReverseBlockReachabilityAnalysis'.

This rename serves two purposes:

- It reflects the actual functionality of this analysis.
- We will have more than one reachability analysis.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@127930 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed