removed warnings from tests

test/optional_test_ref_fail_init_from_Trefref.cpp

@@ -10,6 +10,7 @@
 //  akrzemi1@gmail.com
 //
 #include "boost/optional.hpp"
+#include "boost/core/ignore_unused.hpp"
 
 #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
 //
@@ -18,6 +19,7 @@
 void optional_reference__test_no_init_from_Trefref()
 {
   boost::optional<const int&> opt = int(3);
+  boost::ignore_unused(opt);
 }
 
 #else