also test sysv64 ABI

Author: RalfJung

tests/codegen/abi-win64-zst.rs

@@ -17,12 +17,16 @@
 #[lang = "sized"]
 trait Sized {}
 
-// Make sure the argument is always ignored when explicitly requesting "win64" ABI.
+// Make sure the argument is always ignored when explicitly requesting "win64" or "sysv64" ABI.
 
 // CHECK: define win64cc void @pass_zst_win64()
 #[no_mangle]
 extern "win64" fn pass_zst_win64(_: ()) {}
 
+// CHECK: define x86_64_sysvcc void @pass_zst_sysv64()
+#[no_mangle]
+extern "sysv64" fn pass_zst_sysv64(_: ()) {}
+
 // For `extern "C"` functions, ZST are *not* ignored on windows-gnu.
 // That's likely an accident on their side but the ABI is what it is.