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

Remove i586-pc-windows-msvc

See [MCP 840](https://github.com/rust-lang/compiler-team/issues/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

1 files changed, 9 insertions, 2 deletions

diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 72202129f5b..15936c731ea 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -1915,7 +1915,6 @@ supported_targets! {
     ("i686-pc-windows-msvc", i686_pc_windows_msvc),
     ("i686-uwp-windows-msvc", i686_uwp_windows_msvc),
     ("i686-win7-windows-msvc", i686_win7_windows_msvc),
-    ("i586-pc-windows-msvc", i586_pc_windows_msvc),
     ("thumbv7a-pc-windows-msvc", thumbv7a_pc_windows_msvc),
     ("thumbv7a-uwp-windows-msvc", thumbv7a_uwp_windows_msvc),
 
@@ -3503,7 +3502,15 @@ impl Target {
                     return load_file(&p);
                 }
 
-                Err(format!("Could not find specification for target {target_tuple:?}"))
+                // Leave in a specialized error message for the removed target.
+                // FIXME: If you see this and it's been a few months after this has been released,
+                // you can probably remove it.
+                if target_tuple == "i586-pc-windows-msvc" {
+                    Err("the `i586-pc-windows-msvc` target has been removed. Use the `i686-pc-windows-msvc` target instead.\n\
+                        Windows 10 (the minimum required OS version) requires a CPU baseline of at least i686 so you can safely switch".into())
+                } else {
+                    Err(format!("Could not find specification for target {target_tuple:?}"))
+                }
             }
             TargetTuple::TargetJson { ref contents, .. } => {
                 let obj = serde_json::from_str(contents).map_err(|e| e.to_string())?;