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/libc/bionic/__cxa_thread_atexit_impl.cpp b/libc/bionic/__cxa_thread_atexit_impl.cpp
index 9ae6dfd..0e427d3 100644
--- a/libc/bionic/__cxa_thread_atexit_impl.cpp
+++ b/libc/bionic/__cxa_thread_atexit_impl.cpp
@@ -22,7 +22,7 @@
   thread_local_dtor* next;
 };
 
-__thread thread_local_dtor* thread_local_dtors = nullptr;
+static __thread thread_local_dtor* thread_local_dtors = nullptr;
 
 extern "C" int __cxa_thread_atexit_impl(void (*func) (void *), void *arg, void *dso_handle) {
   thread_local_dtor* dtor = new thread_local_dtor();