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

Source/wtf/Assertions.h

Index: Source/wtf/Assertions.h
diff --git a/Source/wtf/Assertions.h b/Source/wtf/Assertions.h
index 4ac87e79ab1cbfe3ae7c6a4c0be90475ff7b6f6a..d3b13a0c7e39bd01995d75908938210f58d1a887 100644
--- a/Source/wtf/Assertions.h
+++ b/Source/wtf/Assertions.h
@@ -143,11 +143,19 @@ using WTF::FrameToNameScope;
    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