Add known type checker crashers.

Add minimized tests for:
    rdar://problem/27261929
    rdar://problem/27329076

validation-test/Sema/type_checker_crashers/rdar27261929.swift

@@ -0,0 +1,20 @@
+// RUN: not --crash %target-swift-frontend %s -parse
+
+public enum R<V> {
+  case value(V)
+}
+
+public struct P<I, O> {
+  public var run: (I) -> R<(O, I)>
+
+  public init(run: @escaping (I) -> R<(O, I)>) {
+    self.run = run
+  }
+
+  public func test() -> P<I, [O]> {
+    return P<I, [O]> { input in
+      var output: [O] = []
+      return R<([O], I)>.value(output, input)
+    }
+  }
+}

validation-test/Sema/type_checker_crashers/rdar27329076.swift

@@ -0,0 +1,3 @@
+// RUN: not --crash %target-swift-frontend %s -parse
+
+_ = try [ { return .D($0[0]) } ]