Rollup merge of #137957 - Noratrieb:no, r=wesleywiser

Remove i586-pc-windows-msvc

See [MCP 840](rust-lang/compiler-team#840).

I left a specialized error message that should help users that hit this in the wild (for example, because they use it in their CI).

```
error: Error loading target specification: the `i586-pc-windows-msvc` target has been removed. Use the `i686-pc-windows-msvc` target instead.
       Windows 10 (the minimum required OS version) requires a CPU baseline of at least i686 so you can safely switch. Run `rustc --print target-list` for a list of built-in targets
```

``@workingjubilee`` ``@calebzulawski`` fyi portable-simd uses this target in CI, if you wanna remove it already before this happens

Author: jhpratt