spin off easy stuff from Herb's windows GN CL

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
@@ skipping 193 matching lines @@
 #endif
 
 //////////////////////////////////////////////////////////////////////
 
 #if !defined(SKIA_IMPLEMENTATION)
     #define SKIA_IMPLEMENTATION 0
 #endif
 
 #if !defined(SK_API)
     #if defined(SKIA_DLL)
-        #if defined(SK_BUILD_FOR_WIN32)
+        #if defined(_MSC_VER)
             #if SKIA_IMPLEMENTATION
                 #define SK_API __declspec(dllexport)
             #else
                 #define SK_API __declspec(dllimport)
             #endif
         #else
             #define SK_API __attribute__((visibility("default")))
         #endif
     #else
         #define SK_API
@@ skipping 38 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