[Testing] unbreak after r372963

llvm-svn: 372967

Author: davezarzycki

libcxxabi/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;