[Bug c++/100157] Support `__type_pack_element` like Clang

[vittorio.romeo at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100157

--- Comment #9 from Vittorio Romeo <vittorio.romeo at outlook dot com> ---
(In reply to Jonathan Wakely from comment #8)
> (In reply to Vittorio Romeo from comment #6)
> > worthwhile to keep the same name as Clang for compatibility,
> 
> No, that's not an option. Clang's is a built-in template, GCC's can't be (it
> would require considerable internal reworking to support that).
> 
> That's also why we have __integer_pack(N)... instead of __make_integer_seq<>.
> 
> Since GCC's built-in has to use different syntax, it would be a disaster to
> use the same name.
> 
> #if __has_builtin(__type_pack_element)
> // now what? is it a template or a function?
> #endif

Got it, I didn't realize that they had to be wildly different. I guess that as
long as a library developer can wrap either under a portable macro, it should
be fine.