Rollup merge of #121237 - Urgau:better-cargo-heuristic, r=compiler-errors

Use better heuristic for printing Cargo specific diagnostics

It was [reported](https://github.com/rust-lang/rust/issues/82450#issuecomment-1948574677) in the check-cfg call for testing that the Rust for Linux project is setting the `CARGO` env without compiling with it, which is an issue since we are using the `CARGO` env as a proxy for "was launched from Cargo".

This PR switch to the `CARGO_CRATE_NAME` [Cargo env](https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates), which shouldn't collide (as much) with other build systems. I also took the opportunity to consolidate all the checks under the same function.

1 files changed, 5 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index 3d7903b5efb..e42a8bd9ed9 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -362,8 +362,11 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for LinkingFailed<'_> {
         // which by now we have no way to translate.
         if contains_undefined_ref {
             diag.note(fluent::codegen_ssa_extern_funcs_not_found)
-                .note(fluent::codegen_ssa_specify_libraries_to_link)
-                .note(fluent::codegen_ssa_use_cargo_directive);
+                .note(fluent::codegen_ssa_specify_libraries_to_link);
+
+            if rustc_session::utils::was_invoked_from_cargo() {
+                diag.note(fluent::codegen_ssa_use_cargo_directive);
+            }
         }
         diag
     }