Add strchrnul.

Bug: http://b/18374026
Change-Id: Iea923309c090a51a2d41c5a83320ab3789f40f1c
diff --git a/libc/libc.map b/libc/libc.map
index 4670079..9456920 100644
--- a/libc/libc.map
+++ b/libc/libc.map
@@ -1342,6 +1342,7 @@
     __write_chk;
     getgrgid_r;
     getgrnam_r;
+    strchrnul;
 } LIBC;
 
 LIBC_PRIVATE {