Auto merge of #119088 - George-lewis:glewis/suggest-upgrading-compiler, r=Nilstrieb

Suggest Upgrading Compiler for Gated Features

This PR addresses #117318

I have a few questions:

1. Do we want to specify the current version and release date of the compiler? I have added this in via environment variables, which I found in the code for the rustc cli where it handles the `--version` flag
  a. How can I handle the changing message in the tests?
3. Do we want to only show this message when the compiler is old?
  a. How can we determine when the compiler is old?

I'll wait until we figure out the message to bless the tests

compiler/rustc_hir_analysis/src/lib.rs

@@ -134,13 +134,8 @@ fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi
         // Using this ABI would be ok, if the feature for additional ABI support was enabled.
         // Return CONVENTIONS_STABLE, because we want the other error to look the same.
         (false, true) => {
-            feature_err(
-                &tcx.sess.parse_sess,
-                sym::extended_varargs_abi_support,
-                span,
-                UNSTABLE_EXPLAIN,
-            )
-            .emit();
+            feature_err(&tcx.sess, sym::extended_varargs_abi_support, span, UNSTABLE_EXPLAIN)
+                .emit();
             CONVENTIONS_STABLE
         }