libc++-20 removes std::__compressed_pair

[benine203]

folly/folly/memory/UninitializedMemoryHacks.h

Line 312 in abf77ba

std::__compressed_pair<pointer, allocator_type> __end_cap_;

for instance references this

From libc++-20:

// Historically, libc++ used a type called `__compressed_pair` to reduce storage needs in cases of empty types (e.g. an
// empty allocator in std::vector). We switched to using `[[no_unique_address]]`. However, for ABI compatibility reasons
// we had to add artificial padding in a few places.
//
// This setting disables the addition of such artificial padding, leading to a more optimal
// representation for several types.
#  define _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING

Failures ensue:

$ clang++ -stdlib=libc++ <...>
.
.
.
build/vcpkg_installed/x64-linux/include/folly/memory/UninitializedMemoryHacks.h:319:8: error: no template named '__compressed_pair' in namespace 'std'
  319 |   std::__compressed_pair<pointer, allocator_type> __end_cap_;
      |   ~~~~~^
1 error generated.