llvm-project

3bb903e3 - [libc++] Treat P0513R0 as a defect report against C++11 (#166690)

[libc++] Treat P0513R0 as a defect report against C++11 (#166690) P0513R0 is essentially a collective resolution paper of LWG2543, LWG2791, LWG2809, and LWG2817. Among these LWG issues, LWG2543 (conditionally enabled `hash`) and LWG2817 (`hash<nullptr_t>`) affect pre-C++17 utilities. We generally backport changes from LWG issues, so this patch backports the relevant parts of P0513R0. Although we provide `hash<unique_ptr>` as an extension in C++03 mode, as C++03 mode isn't encouraged now, this patch leaves `hash<unique_ptr>` unchanged in C++03 mode.