clang on windows support

1) Run python bin/fetch-clang-win
2) Set clang_win = "../bin/clang_win"
3) ???
4) Profit

Most changes here are to pass the right -mfoo flags to Clang
to enable advanced instruction sets, or fixed warning-as-errors.

BUG=skia:2679

Change-Id: Ieed145d35c209131c7c16fdd3ee11a3de4a1a921
Reviewed-on: https://skia-review.googlesource.com/28740
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/src/ports/SkImageEncoder_WIC.cpp b/src/ports/SkImageEncoder_WIC.cpp
index 1ae9257..dc51604 100644
--- a/src/ports/SkImageEncoder_WIC.cpp
+++ b/src/ports/SkImageEncoder_WIC.cpp
@@ -159,7 +159,7 @@
         PROPBAG2 name = { 0 };
         name.dwType = PROPBAG2_TYPE_DATA;
         name.vt = VT_R4;
-        name.pstrName = L"ImageQuality";
+        name.pstrName = const_cast<LPOLESTR>(L"ImageQuality");
 
         VARIANT value;
         VariantInit(&value);