[Bug c/116728] c23 tag compatibility broken with pointers to incomplete types

[himehaieto at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116728

--- Comment #2 from Hime Haieto <himehaieto at gmail dot com> ---
This may not actually be about pointer issues specifically - I came across
another failing test case that I think is most likely caused by the same
underlying issue:

typedef void f(struct s1);
struct s1 {
        int f1;
};
typedef void f(struct s1);