Dont cast away const needlessly. Found by gcc48 -Wcast-qual.

llvm-svn: 163325
diff --git a/clang/lib/Analysis/ReachableCode.cpp b/clang/lib/Analysis/ReachableCode.cpp
index bb63e2c..11f2ebe 100644
--- a/clang/lib/Analysis/ReachableCode.cpp
+++ b/clang/lib/Analysis/ReachableCode.cpp
@@ -112,8 +112,8 @@
 
 static int SrcCmp(const void *p1, const void *p2) {
   return
-    ((std::pair<const CFGBlock *, const Stmt *>*) p2)->second->getLocStart() <
-    ((std::pair<const CFGBlock *, const Stmt *>*) p1)->second->getLocStart();
+    ((const std::pair<const CFGBlock *, const Stmt *>*) p2)->second->getLocStart() <
+    ((const std::pair<const CFGBlock *, const Stmt *>*) p1)->second->getLocStart();
 }
 
 unsigned DeadCodeScan::scanBackwards(const clang::CFGBlock *Start,