libstdc++: Uncomment checks for <limits> enumeration types

I don't know why these checks are disabled.

libstdc++-v3/ChangeLog:

	* testsuite/18_support/headers/limits/synopsis.cc: Uncomment
	checks for float_round_style and float_denorm_style.

libstdc++-v3/testsuite/18_support/headers/limits/synopsis.cc

@@ -23,10 +23,8 @@
 namespace std {
   template<class T> class numeric_limits;
 
-#if 0
   enum float_round_style;
   enum float_denorm_style;
-#endif
 
   template<> class numeric_limits<bool>;