Add regression test for fixed crasher

Author: slavapestov

validation-test/compiler_crashers_2_fixed/rdar57728533.swift

@@ -0,0 +1,10 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+protocol Item {
+  associatedtype Rule
+  func isValide(valid: Rule) -> Bool
+}
+
+protocol PairableItem: Item {
+  associatedtype AssociatedItem: PairableItem where AssociatedItem.Rule: Rule
+}