Missing header


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353933 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/ADT/OptionalTest.cpp b/unittests/ADT/OptionalTest.cpp
index 8d49b3d..c39b672 100644
--- a/unittests/ADT/OptionalTest.cpp
+++ b/unittests/ADT/OptionalTest.cpp
@@ -12,6 +12,8 @@
 #include "gtest/gtest-spi.h"
 #include "gtest/gtest.h"
 
+#include <array>
+
 using namespace llvm;
 
 namespace {