gccrs: [E0045] Variadic Parameters Used on Non-C ABI Function

Added error code support for using variadic parameters used
on Non-C ABI function. Fixes Rust-GCC#2382

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-implitem.cc (TypeCheckTopLevelExternItem::visit):
	Added check for error code support.

gcc/testsuite/ChangeLog:

	* rust/compile/abi-vardaic.rs: New test.

Signed-off-by: Muhammad Mahad <mahadtxt@gmail.com>

gcc/rust/typecheck/rust-hir-type-check-implitem.cc

@@ -138,7 +138,15 @@ TypeCheckTopLevelExternItem::visit (HIR::ExternalFunctionItem &function)
 
   uint8_t flags = TyTy::FnType::FNTYPE_IS_EXTERN_FLAG;
   if (function.is_variadic ())
-    flags |= TyTy::FnType::FNTYPE_IS_VARADIC_FLAG;
+    {
+      flags |= TyTy::FnType::FNTYPE_IS_VARADIC_FLAG;
+      if (parent.get_abi () != Rust::ABI::C)
+	{
+	  rust_error_at (
+	    function.get_locus (), ErrorCode ("E0045"),
+	    "C-variadic function must have C or cdecl calling convention");
+	}
+    }
 
   RustIdent ident{
     CanonicalPath::new_seg (function.get_mappings ().get_nodeid (),

gcc/testsuite/rust/compile/abi-vardaic.rs

@@ -0,0 +1,7 @@
+// https://doc.rust-lang.org/error_codes/E0045.html
+#![allow(unused)]
+fn main() {
+    extern "Rust" {
+        fn foo(x: u8, ...); // { dg-error "C-variadic function must have C or cdecl calling convention" }
+    }
+}