Warning: <type> is not FFI-safe, after recent changes involving `#[non_exhaustive]`

After the recent commit (9ee2d2a0f6180e092ada3f9a5960a31b290fa755) in which I added #[non_exhaustive] to kproc_info on FreeBSD 15, I get warnings like the following when I run libc-test:

warning: `extern` block uses type `libc::kinfo_proc`, which is not FFI-safe
      --> /home/jn/libc/target/debug/build/libc-test-9d66e31a05563bd6/out/ctest_output.rs:132002:62
       |
132002 |             fn ctest_field_ptr__kinfo_proc__ki_structsize(a: *const kinfo_proc) -> *mut u8;
       |                                                              ^^^^^^^^^^^^^^^^^ not FFI-safe
       |
       = note: this struct is non-exhaustive
       = note: `#[warn(improper_ctypes)]` on by default

This seems to point to a larger problem with using #[non_exhaustive] in the libc crate.

cc @tgross35

Start by reviewing commit 9ee2d2a0f6180e092ada3f9a5960a31b290fa755 and reproducing the warning with libc-test. Inspect the generated ctest_output.rs references to kinfo_proc and determine how #[non_exhaustive] affects the FFI bindings. Done means establishing and implementing an FFI-safe resolution for the reported warnings, though the issue does not define a specific fix.