Merge pull request #17739 from slavapestov/fixed-crasher-testcase

Add test case for crasher that's already fixed on master

Author: slavapestov

validation-test/compiler_crashers_2_fixed/0167-rdar39059582.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend %s -emit-ir
+
+protocol X {
+  associatedtype R : Y
+}
+
+protocol Y {
+  associatedtype Q : X where Q.R == Self
+}
+
+struct B : Y {
+  typealias Q = L<B> 
+}
+
+struct L<V : Y> : X {
+  typealias R = V
+}