make the sourcemgr available through ASTContext.

llvm-svn: 41906
diff --git a/clang/Analysis/DeadStores.cpp b/clang/Analysis/DeadStores.cpp
index 91034e3..e898f3c 100644
--- a/clang/Analysis/DeadStores.cpp
+++ b/clang/Analysis/DeadStores.cpp
@@ -29,7 +29,9 @@
   ASTContext Ctx;
 public:
   DeadStoreObserver(Preprocessor& pp) : 
-    PP(pp), Ctx(PP.getTargetInfo(), PP.getIdentifierTable()) {}
+    PP(pp), Ctx(PP.getSourceManager(), PP.getTargetInfo(),
+                PP.getIdentifierTable()) {
+  }
     
   virtual ~DeadStoreObserver() {}