[PATCH] D45179: [libc++] Add _LIBCPP_ENABLE_NODISCARD and _LIBCPP_NODISCARD_EXT to allow pre-C++2a [[nodiscard]]

[Eric Fiselier via Phabricator via cfe-commits]

EricWF added a comment.

A couple other notes:

- Add an application of `_LIBCPP_NODISCARD_EXT` to `get_temporary_buffer` to demonstrate usage.


https://reviews.llvm.org/D45179