Hide __set_tls.

Bug: 11156955
Change-Id: If82c10ae412651361d09591017d1c3a411bd6f0b
diff --git a/libc/arch-x86/bionic/__set_tls.c b/libc/arch-x86/bionic/__set_tls.c
index 722ec6f..38ed3c9 100644
--- a/libc/arch-x86/bionic/__set_tls.c
+++ b/libc/arch-x86/bionic/__set_tls.c
@@ -57,7 +57,7 @@
   result->useable = 1;
 }
 
-int __set_tls(void* ptr) {
+__LIBC_HIDDEN__ int __set_tls(void* ptr) {
   struct user_desc tls_descriptor;
   __init_user_desc(&tls_descriptor, true, ptr);