Auto merge of #113730 - belovdv:jobserver-init-check, r=petrochenkov

Report errors in jobserver inherited through environment variables

This pr attempts to catch situations, when jobserver exists, but is not being inherited.

r? `@petrochenkov`

Author: bors

cargo-miri/src/phases.rs

@@ -501,6 +501,14 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
     // Set missing env vars. We prefer build-time env vars over run-time ones; see
     // <https://github.com/rust-lang/miri/issues/1661> for the kind of issue that fixes.
     for (name, val) in info.env {
+        // `CARGO_MAKEFLAGS` contains information about how to reach the
+        // jobserver, but by the time the program is being run, that jobserver
+        // no longer exists. Hence we shouldn't forward this.
+        // FIXME: Miri builds the final crate without a jobserver.
+        // This may be fixed with github.com/rust-lang/cargo/issues/12597.
+        if name == "CARGO_MAKEFLAGS" {
+            continue;
+        }
         if let Some(old_val) = env::var_os(&name) {
             if old_val == val {
                 // This one did not actually change, no need to re-set it.