Cast 3.14f to float because FLT_EVAL_METHOD (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108742) for discussion

test/variant_visit_r.cpp

@@ -72,7 +72,7 @@ int main()
         variant<int, float> const v2( 3.14f );
 
         BOOST_TEST_EQ( visit<int>( F2(), v1, v2 ), 4 );
-        BOOST_TEST_EQ( visit<float>( F2(), v1, v2 ), 1 + 3.14f );
+        BOOST_TEST_EQ( visit<float>( F2(), v1, v2 ), static_cast<float>( 1 + 3.14f ) ); // see FLT_EVAL_METHOD
     }
 
     {