Move linker-namespace functions to LIBC_PLATFORM

Bug: http://b/28174921
Change-Id: I089dbeeea813fc2128b9c2f6268a578d23a1954a
diff --git a/libdl/libdl.arm64.map b/libdl/libdl.arm64.map
index 0a5ac97..f21859c 100644
--- a/libdl/libdl.arm64.map
+++ b/libdl/libdl.arm64.map
@@ -15,8 +15,6 @@
 
 LIBC_N {
   global:
-    android_init_namespaces;
-    android_create_namespace;
     dlvsym;
 } LIBC;
 
@@ -27,4 +25,6 @@
     android_set_application_target_sdk_version;
     android_get_LD_LIBRARY_PATH;
     android_update_LD_LIBRARY_PATH;
+    android_init_namespaces;
+    android_create_namespace;
 } LIBC_N;