turn on extended Clang warnings on Windows too

Plus some small rearrangements of the various warning lists.

Change-Id: Ied58f940341d69ddab971a529fd01b1e96b65641
Reviewed-on: https://skia-review.googlesource.com/67720
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/samplecode/SampleBigGradient.cpp b/samplecode/SampleBigGradient.cpp
index 301c3d8..c174f6e 100644
--- a/samplecode/SampleBigGradient.cpp
+++ b/samplecode/SampleBigGradient.cpp
@@ -186,7 +186,8 @@
 // required so that we can call the base class' constructor with the pixel
 // data.
 static bool Create(int width, int height, bool is_opaque, SkRasterHandleAllocator::Rec* rec) {
-    BITMAPINFOHEADER hdr = { 0 };
+    BITMAPINFOHEADER hdr;
+    memset(&hdr, 0, sizeof(hdr));
     hdr.biSize = sizeof(BITMAPINFOHEADER);
     hdr.biWidth = width;
     hdr.biHeight = -height;  // Minus means top-down bitmap.