Merge pull request #5643 from practicalswift/swiftc-28468-segfault-0xd09050-0xd08dfd-0xbe9d76-0xbeb154

[swiftc (98 vs. 5181)] Add crasher in swift::TypeBase::getCanonicalType(...)

Author: practicalswift

validation-test/compiler_crashers/28468-segfault-0xd09050-0xd08dfd-0xbe9d76-0xbeb154.swift

@@ -0,0 +1,9 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// RUN: not --crash %target-swift-frontend %s -emit-ir
+protocol A{typealias B>typealias B<a>:a}extension A