- Update to version 0.21, update LLVM/Clang to version 17.
* Improve analysis of type aliases (typedef and using).
* Improve analysis of namespace aliases (namespace xyz = foobar).
* Improve support for elaborated forward declarations
(typedef struct Foo Bar).
* Improve handling of "autocast" and function return types,
particularly with complex template types.
* Add new IWYU pragma: always_keep, which lets a header announce
that it should always be kept wherever included.
* Automatically use builtin libc++ mappings if libc++ is the
active standard library.
* Improve mappings for libc++ and posix headers.
- Rebase iwyu_include_picker.patch.