gccrs: testsuite/rust: add a testcase for testing ...

... builtin macro and decl macro mixed expansion

gcc/testsuite/ChangeLog:

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

Signed-off-by: Zixing Liu <liushuyu011@gmail.com>

gcc/testsuite/rust/compile/builtin_macro_recurse.rs

@@ -0,0 +1,21 @@
+// { dg-additional-options "-fdump-tree-gimple" }
+
+#[rustc_builtin_macro]
+macro_rules! concat {
+    () => {{}};
+}
+
+macro_rules! a {
+    () => { "test" };
+}
+
+macro_rules! b {
+    () => { "canary" };
+}
+
+fn main() {
+    // { dg-final { scan-tree-dump-times {"test1canary"} 1 gimple } }
+    let _ = concat!(a!(), 1, b!());
+    // should not error
+    concat!(a!(), true, b!(),);
+}