NativeCallInfo: add toString

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

@@ -22,6 +22,7 @@
  */
 package com.oracle.truffle.r.runtime.ffi;
 
+import com.oracle.truffle.api.CompilerAsserts;
 import com.oracle.truffle.api.CompilerDirectives.ValueType;
 import com.oracle.truffle.r.runtime.data.RList;
 import com.oracle.truffle.r.runtime.ffi.DLL.DLLInfo;
@@ -42,4 +43,10 @@ public final class NativeCallInfo {
         this.address = address;
         this.dllInfo = dllInfo;
     }
+
+    @Override
+    public String toString() {
+        CompilerAsserts.neverPartOfCompilation();
+        return String.format("dll: %s, name: %s", dllInfo.name, name);
+    }
 }