[PATCH] [libcxx] Remove use of default function template parameters in type traits. Fixes DR20484

[Marshall Clow]

I tested this in C++03/11/14 modes. All tests passed in 11/14, but the is_destructible tests failed in C++03 mode (as they did before this change), due to the fact that __typeof__ is not really a replacement for declval. 

This looks OK to me.

================
Comment at: include/type_traits:1554
@@ +1553,3 @@
+	static char  __test (
+        typename __is_destructible_apply<decltype(_VSTD::declval<_Tp1&>().~_Tp1())>::type
+    );
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Agustín Bergé wrote:
> Isn't the `decltype` still a problem if it has to compile in C++03 mode?
Yes. It will fail (cause a compilation failure) when the destructor is private or protected.

http://reviews.llvm.org/D4735