Avoid unsed variable in test for MSVC 2015

Author: Flamefire

test/test_mock.cpp

@@ -364,7 +364,8 @@ MOCK_BASE_CLASS(variadic, base)
 void instantiate_class()
 {
     variadic inst; // If this compiles all pure virtual methods were mocked
-    BOOST_ATTRIBUTE_UNUSED const variadic& cinst = inst;
+    const variadic& cinst = inst;
+    (void) cinst; // Avoid unused variable warning
     static_assert(noexcept(inst.m12()), "noexcept should be kept");
     static_assert(!noexcept(inst.m14()), "noexcept should not be set");
     static_assert(noexcept(cinst.m14(1)), "noexcept should be kept");