test that the abi of c-variadic functions is checked in extern blocks

tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs

@@ -13,4 +13,19 @@ fn win(f: extern "win64" fn(usize, ...)) {
     f(22, 44);
 }
 
+extern "efiapi" {
+    fn extern_efiapi(...);
+    //~^ ERROR using calling conventions other than `C` or `cdecl` for varargs functions is unstable [E0658]
+}
+
+extern "sysv64" {
+    fn extern_sysv64(...);
+    //~^ ERROR using calling conventions other than `C` or `cdecl` for varargs functions is unstable [E0658]
+}
+
+extern "win64" {
+    fn extern_win64(...);
+    //~^ ERROR using calling conventions other than `C` or `cdecl` for varargs functions is unstable [E0658]
+}
+
 fn main() {}

tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.stderr

@@ -28,6 +28,36 @@ LL | fn win(f: extern "win64" fn(usize, ...)) {
    = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 3 previous errors
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:17:5
+   |
+LL |     fn extern_efiapi(...);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
+   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:22:5
+   |
+LL |     fn extern_sysv64(...);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
+   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:27:5
+   |
+LL |     fn extern_win64(...);
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
+   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0658`.