[Bug c++/109877] Support for clang-style attributes is needed to parse Darwin SDK headers properly

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109877

--- Comment #8 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #7)
> can we fixinclude the headers?

1. not yet (PR105719) - although let us hope we can find a way to do that for
more limited cases (I've implemented the consumer code, but the generation and
install side is more work).

2. In any event, (especially for 'availability') that would be a huge job
(essentially re-writing a significant bunch of framework and /usr/include
cases), and keeping up with frequent Xcode / SDK updates would be quite a
maintenance burden***.

3. It does not help our downstream to use other projects which make use of
these features (in non-SDK sources).

----

*** other options considered:

for "closed" SDKs for system versions out of vendor support, I suppose we could
just have a script that sed'ed the headers into a replacement, but that is
still some machinery to implement.

It would be nice to have an open SDK - but that is a huge project in its own
right, and likewise would need someone with time to maintain the bleeding edge
version