Add two passing regression tests and a failing one

Author: slavapestov

validation-test/compiler_crashers_2/sr13849.swift

@@ -0,0 +1,13 @@
+// RUN: not --crash %target-swift-frontend -emit-ir %s
+
+public protocol Prot {
+    associatedtype T
+}
+
+public class C<P: Prot> where P.T: Hashable {
+}
+
+public class Spam<P: Prot> where P.T == Int {
+    public func m(_ f: (C<P>) -> C<P>) {
+    }
+}

validation-test/compiler_crashers_2_fixed/rdar65297215.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+public protocol LinkedListNode: AnyObject {
+    associatedtype T
+}
+
+public class LinkedList<N: LinkedListNode> where N.T: Hashable {
+    public typealias T = N.T
+}
+
+public struct LinkedListIterator<N: LinkedListNode>: IteratorProtocol {
+    public mutating func next() -> N.T? {
+      return nil
+    }
+}
+
+extension LinkedList: Sequence {
+    public typealias Element = T
+    public typealias Iterator = LinkedListIterator<N>
+    public __consuming func makeIterator() -> Iterator {
+        fatalError()
+    }
+}

validation-test/compiler_crashers_2_fixed/rdar69073431.swift

@@ -0,0 +1,11 @@
+// RUN: %target-swift-frontend -emit-ir %s
+// REQUIRES: OS=macosx
+
+import Combine
+
+@available(macOS 10.15, *)
+extension Publishers.Share {
+    func foo<A: Publisher, B: Publisher>() where Upstream == Publishers.FlatMap<A, B>, B.Output == UInt8 {
+        
+    }
+}