Maintenance: Add missing header include guards (microsoft#155)

Author: bgianfo

samples/dtest/dtarge.h

@@ -6,6 +6,7 @@
 //
 //  Copyright (c) Microsoft Corporation.  All rights reserved.
 //
+#pragma once
 
 #if (_MSC_VER < 1299)
 typedef DWORD DWORD_PTR;

samples/findfunc/target.h

@@ -6,6 +6,7 @@
 //
 //  Copyright (c) Microsoft Corporation.  All rights reserved.
 //
+#pragma once
 
 DWORD WINAPI Target(DWORD dwCount);
 

samples/slept/slept.h

@@ -6,6 +6,7 @@
 //
 //  Copyright (c) Microsoft Corporation.  All rights reserved.
 //
+#pragma once
 
 DWORD WINAPI UntimedSleepEx(DWORD dwMilliseconds, BOOL bAlertable);
 DWORD WINAPI TimedSleepEx(DWORD dwMilliseconds, BOOL bAlertable);

tests/corruptor.h

@@ -6,6 +6,8 @@
 //
 //  Copyright (c) Microsoft Corporation.  All rights reserved.
 //
+#pragma once
+
 class ImageCorruptor final
 {
 public: