To rephrase adrianN's comment:

It wouldn't mean breaking things on compilers other than GCC. It would simply add compile-time checks when building with GCC, and would do nothing on other compilers.

Wanting code to compile on something other than gcc is not "caring too much", it's being responsible

For this particular case it wouldn't be a big deal. The code is still valid C, it's just that GCC makes sure that you don't use the poisoned values.

Responsible? What an hyperbolic statement. Could you enlighten me on what would be the significant negative consequences? I hope that your mental equation take into account the missed usefulness of GCC only attributes, flags and extensions by being clang compatible.

I don't know what to tell you. Do you think all compilers should implement all GCC proprietary extensions, basically creating a parallel C standard?

And that's not saying that GCC extensions are not useful, but they should not be considered the norm

Agreed. But I wonder if we already have a sort of parallel C standard already with POSIX (of course the parts about C, not about OS facilities).