Define the NO_SANITIZE_ADDRESS macro in a 'clang-cl /fallback' friendly way

Source/platform/heap/AddressSanitizer.h

 /*
  * Copyright (C) 2014 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 16 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef AddressSanitizer_h
 #define AddressSanitizer_h
 
 // FIXME: Add SyZyASan support?
 #if defined(ADDRESS_SANITIZER)
 #include <sanitizer/asan_interface.h>
-#define NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
 #else
 #define ASAN_POISON_MEMORY_REGION(addr, size)   \
     ((void)(addr), (void)(size))
 #define ASAN_UNPOISON_MEMORY_REGION(addr, size) \
     ((void)(addr), (void)(size))
+#endif
+
+// FIXME: Have to handle (ADDRESS_SANITIZER && _WIN32) differently as it uses
+// both Clang (which supports the __attribute__ syntax) and CL (which doesn't)
+// as long as we use "clang-cl /fallback". This shouldn't be needed when Clang
+// handles all the code without falling back to CL.
+#if defined(ADDRESS_SANITIZER) && (!OS(WIN) || COMPILER(CLANG))
+#define NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
+#else
 #define NO_SANITIZE_ADDRESS
 #endif
 
 const size_t asanMagic = 0xabefeed0;
 const size_t asanDeferMemoryReuseCount = 2;
 const size_t asanDeferMemoryReuseMask = 0x3;
 
 #endif