Mark LIBC_O as being a future version.

None of these symbols are in the NDK yet. Skip them.

Change-Id: I946cde38e767190c396593d562babc90457973fb
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 2f613b0..b71739f 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1291,7 +1291,7 @@
     tmpfile64; # introduced=24
 } LIBC;
 
-LIBC_O {
+LIBC_O { # future
   global:
     catclose;
     catgets;