Rollup merge of #116161 - Soveu:varargs2, r=cjgillot

Stabilize `extended_varargs_abi_support`

I think that is everything? If there is any documentation regarding `extern` and/or varargs to correct, let me know, some quick greps suggest that there might be none.

Tracking issue: https://github.com/rust-lang/rust/issues/100189

compiler/rustc_hir_analysis/src/errors.rs

@@ -672,11 +672,10 @@ pub(crate) struct MainFunctionGenericParameters {
 
 #[derive(Diagnostic)]
 #[diag(hir_analysis_variadic_function_compatible_convention, code = E0045)]
-pub(crate) struct VariadicFunctionCompatibleConvention<'a> {
+pub(crate) struct VariadicFunctionCompatibleConvention {
     #[primary_span]
     #[label]
     pub span: Span,
-    pub conventions: &'a str,
 }
 
 #[derive(Diagnostic)]