[Testing] unbreak after r372963

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@372967 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/guard_test_basic.pass.cpp b/test/guard_test_basic.pass.cpp
index a325dd0..7e5b7ac 100644
--- a/test/guard_test_basic.pass.cpp
+++ b/test/guard_test_basic.pass.cpp
@@ -10,6 +10,7 @@
 
 #define TESTING_CXA_GUARD
 #include "../src/cxa_guard_impl.h"
+#include <cassert>
 
 using namespace __cxxabiv1;