gccrs: add testcase with struct to test component_ref and constructor codes..

..in eval_constant_expression()

gcc/testsuite/ChangeLog:

	* rust/compile/const8.rs: New test.

Signed-off-by: Faisal Abbas <90.abbasfaisal@gmail.com>

gcc/testsuite/rust/compile/const8.rs

@@ -0,0 +1,40 @@
+// { dg-options "-w -O0 -fdump-tree-gimple" }
+struct Foo {
+    First: i32,
+    Second: f32
+}
+
+struct Bar {
+    First: i32,
+    Second: f32
+}
+
+struct Baz {
+    First: i32,
+    Second: f32
+}
+const A:Foo = Foo { First: 1, Second: 1.0 };
+const B:Bar = Bar { First: 2, Second: 2.0 };
+const C:Baz = Baz { First: 3, Second: 2.0 };
+
+const fn test() -> f32 {
+    if (A.First == 2) {
+        return A.Second;
+    }
+    else if (B.First == 2) {
+        return B.Second;
+    }
+    else if (C.First == 2) {
+        return C.Second;
+    }
+
+    return 0.0;
+}
+
+const D:f32 = test();
+
+fn main() {
+    // { dg-final { scan-tree-dump-times {d = 2.0} 1 gimple } }
+    let d = D;
+}
+