Add default trait implementations for "c-unwind" ABI function pointers
Following up on #92964, only add default trait implementations for the `c-unwind` family of function pointers. The previous attempt in #92964 added trait implementations for many more ABIs and ran into concerns regarding the increase in size of the libcore rlib.
An attempt to abstract away function pointer types behind a unified trait to reduce the duplication of trait impls is being discussed in #99531 but this change looks to be blocked on a lang MCP.
Following `@RalfJung's` suggestion in https://github.com/rust-lang/rust/pull/99531#issuecomment-1233440142, this commit is another cut at #92964 but it _only_ adds the impls for `extern "C-unwind" fn` and `unsafe extern "C-unwind" fn`.
I am interested in landing this patch to unblock the stabilization of the `c_unwind` feature.
RFC: https://github.com/rust-lang/rfcs/pull/2945
Tracking Issue: https://github.com/rust-lang/rust/issues/74990
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