Auto merge of #118071 - Urgau:check-cfg-cargo-feature, r=petrochenkov

Remove `feature` from the list of well known check-cfg name

This PR removes `feature` from the list of well known check-cfg.

This is done for multiple reasons:
 - Cargo is the source of truth, rustc shouldn't have any knowledge of it
 - It creates a conflict between Cargo and rustc when there are no features defined.
   In this case Cargo won't pass any `--check-cfg` for `feature` since no feature will ever be passed, but rustc by having in it's list adds a implicit `cfg(feature, values(any()))` which is completely wrong. Having any cfg `feature` is unexpected not allow any `feature` value.

While doing this, I took the opportunity to specialise the diagnostic a bit for the case above.

r? `@petrochenkov`

src/bootstrap/src/bin/rustc.rs

@@ -114,7 +114,7 @@ fn main() {
         {
             cmd.arg("-Ztls-model=initial-exec");
         }
-    } else {
+    } else if std::env::var("MIRI").is_err() {
         // Find any host flags that were passed by bootstrap.
         // The flags are stored in a RUSTC_HOST_FLAGS variable, separated by spaces.
         if let Ok(flags) = std::env::var("RUSTC_HOST_FLAGS") {