gccrs: Add another test case for passing associated type-bounds

This demonstrates that this also works for custom algebraic data types too.

gcc/testsuite/ChangeLog:

	* rust/execute/torture/issue-1720-2.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

gcc/testsuite/rust/execute/torture/issue-1720-2.rs

@@ -0,0 +1,30 @@
+mod core {
+    mod ops {
+        #[lang = "add"]
+        pub trait Add<Rhs = Self> {
+            type Output;
+
+            fn add(self, rhs: Rhs) -> Self::Output;
+        }
+    }
+}
+
+struct Foo(i32);
+
+impl core::ops::Add for Foo {
+    type Output = i32;
+
+    fn add(self, rhs: Foo) -> Self::Output {
+        self.0 + rhs.0
+    }
+}
+
+pub fn bar<T: core::ops::Add<Output = i32>>(a: T) -> i32 {
+    a + a
+}
+
+pub fn main() -> i32 {
+    let a = Foo(1);
+
+    bar(a) - 2
+}