Build fails with libc++ from Xcode 27: _LIBCPP_TEMPLATE_VIS is no longer defined

Environment: Xcode 27.0 (27A266a), macOS, x86_64, range-v3 master (108f93c)

Problem: include/meta/meta_fwd.hpp (line ~221) defines META_TEMPLATE_VIS as _LIBCPP_TEMPLATE_VIS when libc++ is used. The libc++ from the Xcode 27 SDK doesn't define that macro anymore, so the preprocessor leaves it as an identifier and the forward declarations of std containers in meta.hpp fail:

meta.hpp:3843:25: error: variable has incomplete type 'class _LIBCPP_TEMPLATE_VIS' meta.hpp:3839:25: error: redefinition of 'unordered_multimap' as different kind of symbol

Workaround: #define META_TEMPLATE_VIS (empty). The build completes.

Possible fix (not tested beyond the workaround above):

cpp
#if defined(_LIBCPP_TEMPLATE_VIS)
#define META_TEMPLATE_VIS _LIBCPP_TEMPLATE_VIS
#else
#define META_TEMPLATE_VIS
#endif

Found while building Telegram Desktop: https://github.com/telegramdesktop/tdesktop/issues/31348