Mark is_destructible/is_nothrow_destructible as implemented

These were implemented back in r244564.  However, I forgot to update the
docs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@253128 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LanguageExtensions.rst

@@ -1017,8 +1017,8 @@ The following type trait primitives are supported by Clang:
   ``argtypes...`` such that no non-trivial functions are called as part of
   that initialization.  This trait is required to implement the C++11 standard
   library.
-* ``__is_destructible`` (MSVC 2013): partially implemented
-* ``__is_nothrow_destructible`` (MSVC 2013): partially implemented
+* ``__is_destructible`` (MSVC 2013)
+* ``__is_nothrow_destructible`` (MSVC 2013)
 * ``__is_nothrow_assignable`` (MSVC 2013, clang)
 * ``__is_constructible`` (MSVC 2013, clang)
 * ``__is_nothrow_constructible`` (MSVC 2013, clang)