a cv-qualifier rvalue reference to the type, e.g.,
template <class _Tp> char __test(const volatile typename remove_reference<_Tp>::type&&);
The use of this function signature rather than the more
straightforward one used in C++98/03 mode, e.g.,
template <class _Tp> char __test(_Tp);
is broken in two ways:
1) An rvalue reference cannot bind to lvalues, so is_convertible<X&,
X&>::value would be false. This breaks two of the unique_ptr tests
on Clang and GCC >= 4.5. Prior GCC's seem to have allowed rvalue
references to bind to lvalues, allowing this bug to slip in.
2) By adding cv-qualifiers to the type we're converting to, we get
some incorrect "true" results for, e.g., is_convertible<const X&, X&>::value.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@124166 91177308-0d34-0410-b5e6-96231b3b80d8
