[Fix] Add missing include from r289444.

llvm-svn: 289446
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index a35b652..c08735d 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -37,6 +37,8 @@
 #include "llvm/Support/Path.h"
 #include "llvm/Transforms/Utils/SanitizerStats.h"
 
+#include <string>
+
 using namespace clang;
 using namespace CodeGen;