Implement pthread spin.

In order to run tsan unit tests, we need to support pthread spin APIs.

Bug: 18623621
Bug: 25392375
Change-Id: Icbb4a74e72e467824b3715982a01600031868e29
diff --git a/libc/libc.arm.map b/libc/libc.arm.map
index f7805fe..69aa272 100644
--- a/libc/libc.arm.map
+++ b/libc/libc.arm.map
@@ -1323,6 +1323,11 @@
     pthread_barrier_destroy;
     pthread_barrier_init;
     pthread_barrier_wait;
+    pthread_spin_destroy;
+    pthread_spin_init;
+    pthread_spin_lock;
+    pthread_spin_trylock;
+    pthread_spin_unlock;
     pwritev;
     pwritev64;
     scandirat;