Debug implemented for __cdecl, but not for __stdcall

[Dushistov]

rustc 1.17.0-nightly (60a0edc 2017-02-26)

Such code compiles fine:

#[repr(C)]
#[derive(Debug)]
pub struct JNINativeInterface_ {
    pub GetVersion: ::std::option::Option<unsafe extern "C" fn(env:
                                                                   *mut ::std::os::raw::c_void)
                                              -> ::std::os::raw::c_int>,
}

fn main() {
}

But if I change "C" to "stdcall" then:

error[E0277]: the trait bound unsafe extern "stdcall" fn(*mut std::os::raw::c_v oid) -> i32: std::fmt::Debug is not satisfied

[petrochenkov]

The reason: #38848 (comment)

[jethrogb]

Close this in favor of more general #40710?