[analyzer] Fix cast-away-const warning by using const_cast.

Patch by David Greene, modified by me.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172445 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h

@@ -167,7 +167,7 @@ namespace ento {
     }
 
     static inline void *MakeVoidPtr(data_type D) {
-      return  (void*) D.getInternalPointer();
+      return const_cast<llvm::ImmutableListImpl<T> >(D.getInternalPointer());
     }
 
     static inline context_type MakeContext(void *p) {