Add pthread_setschedprio.

Bug: http://b/26204555
Test: ran tests
Change-Id: Ic34062b9b6036a1ce2642a069514bab48a893338
diff --git a/libc/libc.arm64.map b/libc/libc.arm64.map
index 5dfe93b..29c5235 100644
--- a/libc/libc.arm64.map
+++ b/libc/libc.arm64.map
@@ -1282,6 +1282,7 @@
     posix_spawn_file_actions_destroy;
     posix_spawn_file_actions_init;
     posix_spawnp;
+    pthread_setschedprio;
     sethostent;
     setnetent;
     setprotoent;