Make SK_BUILD_FOR_WIN32 auto-detection work.

include/core/SkPreConfig.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 // IWYU pragma: private, include "SkTypes.h"
 
 #ifndef SkPreConfig_DEFINED
 #define SkPreConfig_DEFINED
 
 // Allows embedders that want to disable macros that take arguments to just
 // define that symbol to be one of these
 #define SK_NOTHING_ARG1(arg1)
 #define SK_NOTHING_ARG2(arg1, arg2)
 #define SK_NOTHING_ARG3(arg1, arg2, arg3)
 
 //////////////////////////////////////////////////////////////////////
 
 #if !defined(SK_BUILD_FOR_ANDROID) && !defined(SK_BUILD_FOR_IOS) && !defined(SK_BUILD_FOR_WIN32) && !defined(SK_BUILD_FOR_UNIX) && !defined(SK_BUILD_FOR_MAC)
 
     #ifdef __APPLE__
         #include "TargetConditionals.h"
     #endif
 
-    #if defined(WIN32) || defined(__SYMBIAN32__)
+    #if defined(_WIN32) || defined(__SYMBIAN32__)
         #define SK_BUILD_FOR_WIN32
     #elif defined(ANDROID)
         #define SK_BUILD_FOR_ANDROID
     #elif defined(linux) || defined(__linux) || defined(__FreeBSD__) || \
           defined(__OpenBSD__) || defined(__sun) || defined(__NetBSD__) || \
           defined(__DragonFly__) || defined(__Fuchsia__) || \
           defined(__GLIBC__) || defined(__GNU__) || defined(__unix__)
         #define SK_BUILD_FOR_UNIX
     #elif TARGET_OS_IPHONE || TARGET_IPHONE_SIMULATOR
         #define SK_BUILD_FOR_IOS
@@ skipping 225 matching lines @@
  *
  * NOTE: Clang/ARM (r161757) does not support the 'optimize' attribute.
  */
 #if SK_HAS_ATTRIBUTE(optimize)
 #   define SK_ATTRIBUTE_OPTIMIZE_O1 __attribute__((optimize("O1")))
 #else
 #   define SK_ATTRIBUTE_OPTIMIZE_O1 /* nothing */
 #endif
 
 #endif