[XRay] Add missing include to unit test

FDRLoggingTest::MultiThreadedCycling uses std::array so we need to
include the right C++ header and not rely on transitive dependencies.

llvm-svn: 321485

compiler-rt/lib/xray/tests/unit/fdr_logging_test.cc

@@ -13,6 +13,7 @@
 #include "xray_fdr_logging.h"
 #include "gtest/gtest.h"
 
+#include <array>
 #include <fcntl.h>
 #include <iostream>
 #include <sys/mman.h>