> I don't see any remaining benefit in keeping code "compatible" with
> old compilers.

I will note that one of the arguments in favor of retaining
compatibility with non-ANSI C compilers will pretty much never go away
with time: NetBSD likes to support "retrocomputing," and bootstrapping
a port on an old platform can be simpler if you can compile most of
the code with an old compiler.

(This is not something I have a stake in personally, though.)