Rollup merge of #42249 - Mark-Simulacrum:issue-40244, r=eddyb

Allow variadic functions with cdecl calling convention.

Fixes #40244.

src/test/compile-fail/E0045.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 extern "Rust" { fn foo(x: u8, ...); }   //~ ERROR E0045
-                                        //~| NOTE variadics require C calling conventions
+                                        //~| NOTE variadics require C or cdecl calling convention
 
 fn main() {
 }

src/test/compile-fail/variadic-ffi-2.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn baz(f: extern "cdecl" fn(usize, ...)) {
-    //~^ ERROR: variadic function must have C calling convention
+// ignore-arm stdcall isn't suppported
+
+fn baz(f: extern "stdcall" fn(usize, ...)) {
+    //~^ ERROR: variadic function must have C or cdecl calling convention
     f(22, 44);
 }
 

src/test/compile-fail/variadic-ffi.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-extern "cdecl" {
-    fn printf(_: *const u8, ...); //~ ERROR: variadic function must have C calling convention
+// ignore-arm stdcall isn't suppported
+
+extern "stdcall" {
+    fn printf(_: *const u8, ...); //~ ERROR: variadic function must have C or cdecl calling
 }
 
 extern {