Don't print unsupported split-debuginfo modes with `-Zunstable-options` Currently unsupported `split-debuginfo` options are enabled by `-Zunstable-options`, for projects that have `-Zunstable-options` for other reasons this can be [an unexpected interaction](https://github.com/rust-lang/rust-clippy/pull/10516#issuecomment-1562604764) This PR makes it so that `--print split-debuginfo -Zunstable-options` doesn't print unsupported modes, so that a cargo config of e.g. ```toml [profile.dev] split-debuginfo = "unpacked" ``` Would not cause an unsupported mode to be enabled on `x86_64-pc-windows-msvc`