Spurious "infinitely recursive" not ffi-safe warning

[ChrisDenton]

The windows-rs crate is getting a whole bunch of spurious FFI-safe warnings:

 error: `extern` block uses type `*mut CRYPT_PROVIDER_FUNCTIONS`, which is not FFI-safe
  --> crates/libs/sys/src/Windows/Win32/Security/WinTrust/mod.rs:23:131
   |
23 | ...ionid : *mut windows_sys::core::GUID, ppfns : *mut CRYPT_PROVIDER_FUNCTIONS) -> super::super::Foundation:: BOOL);
   |                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
   |
   = note: type is infinitely recursive

error: could not compile `windows-sys` (lib) due to 668 previous errors

See: https://github.com/microsoft/windows-rs/actions/runs/10997420795/job/30532923854?pr=3291

[jieyouxu]

cc #130598 which introduced the recursion limit.

[compiler-errors]

Repro:

#![recursion_limit = "5"]
#![deny(improper_ctypes)]

#[repr(C)]
struct F1(*const ());
#[repr(C)]
struct F2(*const ());
#[repr(C)]
struct F3(*const ());
#[repr(C)]
struct F4(*const ());
#[repr(C)]
struct F5(*const ());
#[repr(C)]
struct F6(*const ());

#[repr(C)]
struct B {
    f1: F1,
    f2: F2,
    f3: F3,
    f4: F4,
    f5: F5,
    f6: F6,
}

extern "C" fn foo(_: B) {}

[compiler-errors]

Anyways I'll put up a revert PR

@rustbot claim