Implement a workaround for thread_local on aarch64

Some versions of lld break thread_local on aarch64. There's a
minimally-painful workaround for it, so let's apply that.

Change-Id: I706de9e280cc15006e5767ee10d961cb2d99352c
diff --git a/aos/testing/BUILD b/aos/testing/BUILD
index 052cabe..ce67b84 100644
--- a/aos/testing/BUILD
+++ b/aos/testing/BUILD
@@ -24,6 +24,7 @@
     visibility = ["//visibility:public"],
     deps = [
         ":googletest",
+        "//aos:thread_local",
         "//aos/logging:implementations",
         "//aos/mutex",
         "@com_google_absl//absl/base",