Consider replacing `extern "stdcall" fn` with `extern "system" fn` where appropriate about com-rs

[bdbai]

Compiling with target thumbv7a-uwp-windows-msvc (a.k.a ARM for Windows Store apps) failed because stdcall is not supported:

error[E0570]: The ABI `"stdcall"` is not supported for the current target
  --> C:\Users\bdbai\.cargo\registry\src\github.com-1ecc6299db9ec823\com-0.2.0\src\interfaces\iclass_factory.rs:12:1
   |
12 | #[com_interface("00000001-0000-0000-c000-000000000046")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0570]: The ABI `"stdcall"` is not supported for the current target
 --> C:\Users\bdbai\.cargo\registry\src\github.com-1ecc6299db9ec823\com-0.2.0\src\interfaces\iunknown.rs:8:1
  |
8 | #[com_interface("00000000-0000-0000-C000-000000000046")]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

Please consider reopening this issue because ARMv7 is still a supported platform on Windows.

[rylev]

Thanks for reporting this. Currently, support for platforms other than Windows is outside the scope of this crate. The intercom crate might be a better fit for that use case at this point. That’s not to say we won’t ever support other platforms, we’re just currently trying to limit the scope to make getting the crate bootstrapped easier. We should make this more explicit in the readme.

[m-hilgendorf]

That's understandable. There's a lot more needed to support cross platform stuff anyway, mostly reexporting what's used from winapi.

[rylev]

I'm going to close this now since this isn't currently on our roadmap, but if we end up supporting other platforms other than Windows, we will definitely make this change.