Add named variadic argument test

Variadic arguments may have a name or a pattern. This commit provides two
new tests in order to ensure their correct behavior.

gcc/testsuite/ChangeLog:

	* rust/compile/pattern_variadic.rs: New test.
	* rust/execute/torture/named_variadic.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

gcc/testsuite/rust/compile/pattern_variadic.rs

@@ -0,0 +1,14 @@
+extern "C" {
+    fn printf(fmt: *const i8, _: ...);
+}
+
+fn main() -> i32 {
+    unsafe {
+        printf(
+            "%s" as *const str as *const i8,
+            "Message" as *const str as *const i8,
+        );
+    }
+
+    0
+}

gcc/testsuite/rust/execute/torture/named_variadic.rs

@@ -0,0 +1,20 @@
+// { dg-output "Named variadic" }
+
+extern "C" {
+    fn printf(fmt: *const i8, variadic: ...);
+}
+
+fn print(s: &str) {
+    unsafe {
+        printf(
+            "%s" as *const str as *const i8,
+            s as *const str as *const i8,
+        );
+    }
+}
+
+fn main() -> i32 {
+    print("Named variadic");
+
+    0
+}