Handle fatal errors for bccRegisterSymbolCallback.

Change-Id: Ifc4e076628c510aee184857e0f8b9df346ad93d7
diff --git a/lib/bcc/bcc.cpp b/lib/bcc/bcc.cpp
index 696b20b..294842b 100644
--- a/lib/bcc/bcc.cpp
+++ b/lib/bcc/bcc.cpp
@@ -68,9 +68,9 @@
   delete unwrap(script);
 }
 
-extern "C" void bccRegisterSymbolCallback(BCCScriptRef script,
-                                          BCCSymbolLookupFn pFn,
-                                          void *pContext) {
+extern "C" int bccRegisterSymbolCallback(BCCScriptRef script,
+                                         BCCSymbolLookupFn pFn,
+                                         void *pContext) {
   BCC_FUNC_LOGGER();
   return unwrap(script)->registerSymbolCallback(pFn, pContext);
 }