Merge pull request #16246 from huonw/rdar37730691

Author: swift-ci

validation-test/compiler_crashers_2_fixed/0157-rdar37730691.swift

@@ -0,0 +1,11 @@
+// RUN: %empty-directory(%t)
+// RUN: not %target-swift-frontend -c %s -index-store-path %t
+
+struct X : Z {
+    func b(_ : Y) {}
+}
+
+protocol Z {
+    associatedtype a
+    typealias Y = a.c
+}