macros: Add test cases for remaining expansion contexts

gcc/testsuite/rust/compile/macro20.rs

@@ -0,0 +1,16 @@
+macro_rules! define_trait {
+    ($assoc:ident, $i:item) => {
+        type $assoc;
+
+        $i
+    };
+}
+
+trait DefinedThroughMacros {
+    define_trait!(
+        Inner,
+        fn takes_inner(i: Self::Inner) -> Self::Inner {
+            i
+        }
+    );
+}

gcc/testsuite/rust/compile/macro21.rs

@@ -0,0 +1,9 @@
+macro_rules! c_fn {
+    {$name:ident ($($arg_name:ident $arg_ty:ty),*) -> $ret_ty:ty} => {
+        fn $name($($arg_name: $arg_ty)*) -> $ret_ty;
+    };
+}
+
+extern "C" {
+    c_fn! {puts (s *const i8) -> i64}
+}

gcc/testsuite/rust/compile/macro22.rs

@@ -0,0 +1,10 @@
+macro_rules! print {
+    () => {
+        fn puts(s: *const i8);
+        fn printf(fmt: *const i8, ...);
+    };
+}
+
+extern "C" {
+    print! {}
+}

gcc/testsuite/rust/compile/macro23.rs

@@ -0,0 +1,25 @@
+macro_rules! maybe_impl {
+    ($left:ident, $right:ident, $l_fn:ident, $r_fn:ident) => {
+        fn $l_fn(value: T) -> Maybe<T> {
+            Maybe::$left(value)
+        }
+
+        fn $r_fn() -> Maybe<T> {
+            Maybe::$right
+        }
+    };
+}
+
+enum Maybe<T> {
+    Just(T),
+    Nothing,
+}
+
+impl<T> Maybe<T> {
+    maybe_impl!(Just, Nothing, just, nothing);
+}
+
+fn main() {
+    let _ = Maybe::just(14);
+    let _: Maybe<i32> = Maybe::nothing();
+}