ART: Add SetSpecialSignalHandlerFn to version-script.txt

Expose the new function from the sigchainlib implementation.

Bug: 20217701
Change-Id: I7d21025595775e057ea703236ca88ceb07173136
diff --git a/sigchainlib/version-script.txt b/sigchainlib/version-script.txt
index ce15054..08c312e 100644
--- a/sigchainlib/version-script.txt
+++ b/sigchainlib/version-script.txt
@@ -5,6 +5,7 @@
   InvokeUserSignalHandler;
   InitializeSignalChain;
   EnsureFrontOfChain;
+  SetSpecialSignalHandlerFn;
   sigaction;
   signal;
   sigprocmask;