Fix tests to work with the new 'FileCheck' substitution

Author: gribozavr

test/Interpreter/SDK/Foundation_NSLog.swift

@@ -5,15 +5,14 @@
 
 // RUN: %target-build-swift %s %t/NSLogIsWorking.o -import-objc-header %t/NSLogIsWorking.h -o %t/main
 // RUN: %target-run %t/main 2>%t/output.txt
-// RUN: (FileCheck %s < %t/output.txt) || (not FileCheck -check-prefix=CHECK-WORKING %s < %t/output.txt)
+// RUN: %FileCheck %s < %t/output.txt
 
 // REQUIRES: executable_test
 // REQUIRES: objc_interop
 
 import Foundation
 
 // CHECK: working
-// CHECK-WORKING: working
 testNSLog()
 
 // CHECK: 1 is the loneliest number that you'll ever do

test/SILOptimizer/devirtualize_existential.swift

@@ -1,4 +1,7 @@
-// RUN: %target-swift-frontend %s -O -emit-sil | not FileCheck %s
+// RUN: %target-swift-frontend %s -O -emit-sil | FileCheck %s
+
+// rdar://problem/27781174
+// XFAIL: *
 
 // FIXME: Existential devirtualization needs to be updated to work with
 // open_existential_addr instructions. rdar://problem/18506660

test/SILOptimizer/specialize_checked_cast_branch.swift

@@ -1,4 +1,7 @@
-// RUN: %target-swift-frontend  -emit-sil -O -sil-inline-threshold 0 %s -o - | not FileCheck %s
+// RUN: %target-swift-frontend  -emit-sil -O -sil-inline-threshold 0 %s -o - | FileCheck %s
+
+// rdar://problem/27781189
+// XFAIL: *
 
 // FIXME: rdar://problem/18603827