tests: remove all -Wall warnings

Author: akrzemi1

test/optional_test_convert_from_T.cpp

@@ -45,6 +45,8 @@ void test_optional_of_superconverting_T() // compile-time test
   superconv<optional<int> > s;
    superconv<optional<int> > & rs = s;
   optional<superconv<optional<int> > > os = rs;
+  (void)s;
+  (void)os;
 #endif
 }
 

test/optional_test_inplace_factory.cpp

@@ -111,10 +111,10 @@ template <typename CharT>
 struct basic_formatter
 {
   template< typename FunT >
-  basic_formatter(FunT&& fun) {}
+  basic_formatter(FunT&&) {}
 
   template< typename FunT >
-  basic_formatter& operator= (FunT&& fun)
+  basic_formatter& operator= (FunT&&)
   {
       return *this;
   }