Add @TruffleBoundary to RFFILog.logNativeObjects.

(cherry picked from commit b6bddc0)

Author: Pavel Marek

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/ffi/RFFILog.java

@@ -124,6 +124,7 @@ private static void logCall(CallMode mode, String name, int depthValue, Object..
         }
     }
 
+    @TruffleBoundary
     private static void logNativeObjects() {
         logPreserveList();
         logProtectStack();