`c_void` has wrong rustc support level in docs

[jethrogb]

The documentation page for core::ffi::c_void says it's available at version 1.1.0, however, it's only available at version 1.30.0.

[Proximyst]

While the module c_void lays in, core::ffi, was stabilised at 1.30.0, the type c_void was stabilised at 1.1.0, which again makes the docs correct. The docs for the module core::ffi say 1.30.0.

[jethrogb]

which again makes the docs correct.

I guess that's a matter of perspective. I think minimum versions of parent items should trickle down to child items such that you don't have to walk up the module tree in the documentation to find out whether something is available or not.

[IsaacWoods]

So I did the original PR to create core::ffi::c_void, and probably agree with @jethrogb in hindsight. The c_void type was originally available at std::os::raw::c_void, which should stay at 1.1.0. However, both std::ffi::c_void and core::ffi::c_void should probably be changed to 1.30.0.

[ExpHP]

This has happened before as well: #49651