Temporarily override the improper_ctypes warning #62.

[rthomas]

The remaining warnings are from types in
core-foundation(CGAffineTransform) and core-graphics(CFNumberRef). When
they are rectified the warnings can be turned back on.

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This change is 

[rthomas]

I really dislike this solution, but I want to dig into the warnings produced by core-foundation and core-graphics first.

I'll need some guidance on the core-foundation work, as this commit reverts the foundation structs to tuple-structs, which seem to be the root cause of the warning.

Alternatively I can investigate whether tuple-structs should actually be triggering this warning to begin with: found zero-size struct in foreign module, consider adding a member to this struct.

[jdm]

We already have the warnings present; why do we need to hide them while we investigate errors in other repositories?

[jdm]

And yes, I think it would be worth talking with the Rust compiler developers about whether types like this should be considered FFI-unsafe:

struct Foo;
struct FooRef(*const Foo);

[jdm]

In fact, the discussion in rust-lang/rust#34798 may be relevant.

[jdm]

Similarly, rust-lang/rust#27303.

[rthomas]

Yeah fair call - I can cancel this PR.

I was reading that discussion along with rust-lang/rust#27303.

It seems odd that the zero-size struct warning is firing for tuple-structs.

[rthomas]

Closing. Warnings are from core-foundation and core-graphics types.