eliminate SK_BUILD_FOR_WIN32

SK_BUILD_FOR_WIN and SK_BUILD_FOR_WIN32 have long meant the same thing.

Chrome fix is https://chromium-review.googlesource.com/c/chromium/src/+/884007

Change-Id: I0e907b1bcd2a358eabf776f414fd3aeb3c689561
Reviewed-on: https://skia-review.googlesource.com/99340
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/src/utils/win/SkIStream.cpp b/src/utils/win/SkIStream.cpp
index 161206f..04d7625 100644
--- a/src/utils/win/SkIStream.cpp
+++ b/src/utils/win/SkIStream.cpp
@@ -6,7 +6,7 @@
  */
 
 #include "SkTypes.h"
-#if defined(SK_BUILD_FOR_WIN32)
+#if defined(SK_BUILD_FOR_WIN)
 
 #include "SkIStream.h"
 #include "SkStream.h"
@@ -271,4 +271,4 @@
     pStatstg->grfMode = STGM_WRITE;
     return S_OK;
 }
-#endif//defined(SK_BUILD_FOR_WIN32)
+#endif//defined(SK_BUILD_FOR_WIN)