gccrs: Add test

gcc/testsuite/ChangeLog:

	* rust/compile/variadic.rs: New test.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>

gcc/testsuite/rust/compile/variadic.rs

@@ -0,0 +1,8 @@
+extern "C" {
+    fn printf(s: *const i8, ...);
+}
+
+fn main() {
+    // { dg-error "expected .c_int. variadic argument" "" { target *-*-* } .+1 }
+    printf("%d\n" as *const str as *const i8, 1i8);
+}