Add renameat2.

Bug: http://b/127675384
Test: new tests
Change-Id: Ia2e3d5679180391ca98e62fa429fa11cbf167507
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 0cab83d..c3b9e2c 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1503,6 +1503,7 @@
     pthread_mutex_clocklock;
     pthread_rwlock_clockrdlock;
     pthread_rwlock_clockwrlock;
+    renameat2;
     sem_clockwait;
     thrd_create;
     thrd_current;