Function referencing in @return? for simplified fault declarations. Check @return? eagerly #2340.

test/test_suite/contracts/contract_copy_optret.c3

@@ -0,0 +1,21 @@
+module test;
+import std;
+
+<*
+ @return? test!
+*>
+fn void? test2()
+{
+	return NOT_FOUND?;
+}
+<*
+ @return? io::EOF, Foo!
+*>
+fn void? test()
+{
+	return NOT_FOUND?;
+}
+<*
+	@return? NOT_FOUND
+*>
+alias Foo = fn void();

test/test_suite/errors/contract_multi.c3

@@ -1,5 +1,5 @@
 module contract_err_tests;
-
+import std;
 <*
 Hello world
  @param [in] a