Fix another GCC build failure from r223802

llvm-svn: 223810
diff --git a/llvm/include/llvm/IR/ValueMap.h b/llvm/include/llvm/IR/ValueMap.h
index 91d09f1..9999113 100644
--- a/llvm/include/llvm/IR/ValueMap.h
+++ b/llvm/include/llvm/IR/ValueMap.h
@@ -33,6 +33,7 @@
 #include "llvm/Support/UniqueLock.h"
 #include "llvm/Support/type_traits.h"
 #include <iterator>
+#include <memory>
 
 namespace llvm {