Hide __libc_init_vdso().

Bug: 11156955
Change-Id: I7ee31e1ee2ce479c5746b374a239637d582815fe
diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index 9e4eecd..ff9940e 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -51,7 +51,7 @@
 extern "C" int __set_tls(void* ptr);
 extern "C" int __set_tid_address(int* tid_address);
 
-void __libc_init_vdso();
+__LIBC_HIDDEN__ void __libc_init_vdso();
 
 // Not public, but well-known in the BSDs.
 const char* __progname;