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
diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp
index 6522d95..bcbf887 100644
--- a/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/lib/Sema/AnalysisBasedWarnings.cpp
@@ -576,7 +576,7 @@
         if (const Stmt *stmt = i->stmt) {
           const CFGBlock *block = AC.getBlockForRegisteredExpression(stmt);
           assert(block);
-          if (CFGReachabilityAnalysis *cra = AC.getCFGReachablityAnalysis()) {
+          if (CFGReverseBlockReachabilityAnalysis *cra = AC.getCFGReachablityAnalysis()) {
             // Can this block be reached from the entrance?
             if (cra->isReachable(&AC.getCFG()->getEntry(), block))
               S.Diag(D.Loc, D.PD);