Re-add the LIBCPP_STATIC_ASSERT

Author: domin144

libcxx/test/std/iterators/iterator.primitives/iterator.traits/cxx20_iterator_traits.compile.pass.cpp

@@ -147,7 +147,8 @@ static_assert(testIOIterator<std::insert_iterator<std::vector<int>>, std::output
 static_assert(testConst<std::istream_iterator<int, char>, std::input_iterator_tag, int>());
 
 #if !defined(TEST_HAS_NO_LOCALIZATION)
-static_assert(test<std::istreambuf_iterator<char>, std::input_iterator_tag, char, std::streamoff, char, char*>());
+// libc++-specific since pointer type is unspecified:
+LIBCPP_STATIC_ASSERT(test<std::istreambuf_iterator<char>, std::input_iterator_tag, char, std::streamoff, char, char*>());
 static_assert(test<std::move_iterator<int*>, std::random_access_iterator_tag, int, std::ptrdiff_t, int&&, int*>());
 static_assert(testIOIterator<std::ostream_iterator<int, char>, std::output_iterator_tag>());
 static_assert(testIOIterator<std::ostreambuf_iterator<int, char>, std::output_iterator_tag>());