Merge pull request #5794 from practicalswift/swiftc-28518-anonymous-namespace-verifier-walktoexprpost-swift-expr

[swiftc (139 vs. 5189)] Add crasher in swift::ASTVisitor

Author: practicalswift

validation-test/compiler_crashers/28518-anonymous-namespace-verifier-walktoexprpost-swift-expr.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
+!(_=nil){}