The macro that opts out of `std::ranges::` functionality is called
`_LIBCPP_HAS_NO_INCOMPLETE_RANGES`, and is unrelated to this macro
which is specifically about _compiler_ support for the _syntax_.
The only non-mechanical diff here is in `<__config>`.
Differential Revision: https://reviews.llvm.org/D118507
We were missing a constraint in common_iterator's iterator_traits and
we were eagerly instantiating iter_value_t even when invalid.
Thanks to Casey Carter for finding this bug.
Differential Revision: https://reviews.llvm.org/D117449