Add test with capitalized Self macro

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3974.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <[email protected]>

Author: P-E-P

gcc/testsuite/rust/compile/issue-3974.rs

@@ -0,0 +1,8 @@
+impl<'a, F> RunUntil<'a, F> {
+    // { dg-error "could not resolve type path" "" { target *-*-* } .-1 }
+    fn project<'pin>() -> Projection<'pin, 'a, F> {
+        // { dg-error "could not resolve type path" "" { target *-*-* } .-1 }
+        Self!()
+        // { dg-error "could not resolve macro invocation" "" { target *-*-* } .-1 }
+    }
+}