To be consistent, make the index of the ElementRegion always signed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@60248 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/RegionStore.cpp b/lib/Analysis/RegionStore.cpp
index 981d69c..1b62cc5 100644
--- a/lib/Analysis/RegionStore.cpp
+++ b/lib/Analysis/RegionStore.cpp
@@ -646,7 +646,7 @@
   nonloc::CompoundVal::iterator VI = CV.begin(), VE = CV.end();
 
   for (; i != Size; ++i) {
-    nonloc::ConcreteInt Idx(getBasicVals().getValue(llvm::APSInt(i)));
+    nonloc::ConcreteInt Idx(getBasicVals().getValue(llvm::APSInt(i, false)));
 
     ElementRegion* ER = MRMgr.getElementRegion(Idx, R);