Fix errors in examples

Author: mborland

examples/charconv.cpp

@@ -18,7 +18,7 @@ int main()
     *r_to.ptr = '\0';
 
     decimal64 return_value;
-    auto r_from = from_chars(buffer, buffer + std::strlen(buffer), return_value);
+    BOOST_DECIMAL_ATTRIBUTE_UNUSED auto r_from = from_chars(buffer, buffer + std::strlen(buffer), return_value);
     assert(r_from);
 
     assert(val == return_value);

examples/rounding_mode.cpp

@@ -7,9 +7,9 @@
 
 int main()
 {
-    auto default_rounding_mode = boost::decimal::fegetround(); // Default is fe_dec_to_nearest_from_zero
+    BOOST_DECIMAL_ATTRIBUTE_UNUSED auto default_rounding_mode = boost::decimal::fegetround(); // Default is fe_dec_to_nearest_from_zero
 
-    auto new_rounding_mode = boost::decimal::fesetround(boost::decimal::rounding_mode::fe_dec_to_nearest);
+    BOOST_DECIMAL_ATTRIBUTE_UNUSED auto new_rounding_mode = boost::decimal::fesetround(boost::decimal::rounding_mode::fe_dec_to_nearest);
 
     assert(default_rounding_mode != new_rounding_mode);