Hide emutls* symbols in libc.so

 Also make thread_local in test static to avoid ld.bfd
 warning for arm64.

Change-Id: I09a3f2aa9b73a4fafa3f3bbc64ddc2a128ad50ee
diff --git a/tests/__cxa_thread_atexit_test.cpp b/tests/__cxa_thread_atexit_test.cpp
index fea60b7..83aab53 100644
--- a/tests/__cxa_thread_atexit_test.cpp
+++ b/tests/__cxa_thread_atexit_test.cpp
@@ -35,7 +35,7 @@
   std::string message;
 };
 
-thread_local ClassWithDtor class_with_dtor;
+static thread_local ClassWithDtor class_with_dtor;
 
 static void* thread_nop(void* arg) {
   class_with_dtor.set_message(*static_cast<std::string*>(arg));