Export our additional C-API functions

Summary:
export the symbol added in D52642782 (will probably be useful later on for other hooks we will want to expose)

using a dedicated `_Ci` prefix to make it obvious which symbols are ABI-changes vs stock

Reviewed By: zsol

Differential Revision: D52643027

fbshipit-source-id: 98a839c02d46866944b52a46f71250aa469fa53d

capi-functions

@@ -3,6 +3,8 @@
     /* Functions defined by Python's C-API */
     Py*;
     _Py*;
+    /* Additional Meta (Cinder) C-API functions to export */
+    _Ci*;
     /* Export strobe symbols needed for pyperf */
     __strobe_*;
   };