Handle new `unexpected_cfgs` warnings

[kennykerr]

Much like https://github.com/tokio-rs/tokio/pull/6538 I need to silence the new warnings introduced by https://github.com/rust-lang/cargo/pull/13571 about unexpected cfg condition names because the alternative is to use a build script which is undesirable and impractical as that introduces a warning about a build script syntax that isn't compatible with the MSRV.

I was able to keep this for most of the crates and further refine code gen to elide code that depended on excluded features.

[epage]

introduces a warning about a build script syntax that isn't compatible with the MSRV.

You can use the : syntax that does work with your MSRV

[kennykerr]

Thanks Ed, I'll give that a try.

[kennykerr]

Weirdly this causes an entirely different warning. No idea why this is coming from the build script.

D:\git\master-rs>cargo check -p windows-targets
   Compiling windows-targets v0.52.5 (D:\git\master-rs\crates\libs\targets)
warning: missing documentation for the crate
 --> crates\libs\targets\build.rs:1:1
  |
1 | / fn main() {
2 | |     println!("cargo:rustc-check-cfg=cfg(windows_raw_dylib)");
3 | | }
  | |_^
  |
  = note: requested on the command line with `-W missing-docs`

[kennykerr]

So I was able to keep this for most of the crates and further refine code gen to elide code that depended on excluded features, which is great. 🎉

I still have to allow the warning for the windows-targets crate due to the unrelated https://github.com/microsoft/windows-rs/pull/3022#issuecomment-2096430603 warning that I've not yet found a workaround for.

[kennykerr]

Looks like the error is coming from the missing_docs workspace lint which is erroneously thinking the windows-targets crate lacks documentation when a build script is added. 🤷