Add const in preparation for a simplify_type change in llvm.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178146 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 4d20467..f20f84c 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -675,7 +675,7 @@
                                    E = BackpatchBlocks.end(); I != E; ++I ) {
 
     CFGBlock *B = I->block;
-    GotoStmt *G = cast<GotoStmt>(B->getTerminator());
+    const GotoStmt *G = cast<GotoStmt>(B->getTerminator());
     LabelMapTy::iterator LI = LabelMap.find(G->getLabel());
 
     // If there is no target for the goto, then we are looking at an