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/tools/skdiff/skdiff_html.cpp b/tools/skdiff/skdiff_html.cpp
index 6f3c3b0..e0476bc 100644
--- a/tools/skdiff/skdiff_html.cpp
+++ b/tools/skdiff/skdiff_html.cpp
@@ -245,7 +245,7 @@
     if (outputDir.size() > 0 && PATH_DIV_CHAR == outputDir[0]) {
         isPathAbsolute = true;
     }
-#ifdef SK_BUILD_FOR_WIN32
+#ifdef SK_BUILD_FOR_WIN
     // On Windows, absolute paths can also start with "x:", where x is any
     // drive letter.
     if (outputDir.size() > 1 && ':' == outputDir[1]) {