Add __builtin_unreachable() to CRASH() when using Clang on Windows.

Source/wtf/Assertions.h

 /*
  * Copyright (C) 2003, 2006, 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 125 matching lines @@
 
 /* CRASH() - Raises a fatal error resulting in program termination and triggering either the debugger or the crash reporter.
 
    Use CRASH() in response to known, unrecoverable errors like out-of-memory.
    Macro is enabled in both debug and release mode.
    To test for unknown errors and verify assumptions, use ASSERT instead, to avoid impacting performance in release builds.
 
    Signals are ignored by the crash reporter on OS X so we must do better.
 */
 #ifndef CRASH
+#if COMPILER(MSVC)
+#if COMPILER(CLANG)
+#define CRASH() (__debugbreak(), __builtin_unreachable())
+#else
+#define CRASH() __debugbreak()
+#endif
+#else
 #define CRASH() \
     (WTFReportBacktrace(), \
      (*(int*)0xfbadbeef = 0), \
      IMMEDIATE_CRASH())
 #endif
+#endif
 
 #if COMPILER(CLANG)
 #define NO_RETURN_DUE_TO_CRASH NO_RETURN
 #else
 #define NO_RETURN_DUE_TO_CRASH
 #endif
 
 /* BACKTRACE
 
   Print a backtrace to the same location as ASSERT messages.
@@ skipping 232 matching lines @@
 } \
 inline const thisType& to##thisType(const argumentType& argumentName) \
 { \
     ASSERT_WITH_SECURITY_IMPLICATION(referencePredicate); \
     return static_cast<const thisType&>(argumentName); \
 } \
 void to##thisType(const thisType*); \
 void to##thisType(const thisType&)
 
 #endif /* WTF_Assertions_h */