Avoid /arch:AVX[2] in Skia on Windows.

skia/BUILD.gn

Index: skia/BUILD.gn
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index c0e296e5fa2f5b3cec2d49e617db10f37f28bdce..1d39c5ce71faa27764a1cf4f614e2a72c3e3a5b3 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -193,6 +193,9 @@ config("skia_library_config") {
                   # assembly code contains flow control(jmp or jcc) statements.
 
       "/wd4800",  # forcing value to bool 'true/false'(assigning int to bool).
+
+      "/wd4752",  # We use AVX but don't let the compiler do so itself.
+                  # See crbug.com/666707.
     ]
   }
 }
@@ -550,11 +553,11 @@ if (!skia_build_no_opts) {
     }
     source_set("skia_opts_avx") {
       sources = skia_opts.avx_sources
-      if (!is_win) {
+      if (!is_win || is_clang) {
         cflags = [ "-mavx" ]

[brucedawson, 2016/11/18 21:00:26]

It feels odd to use -mavx on a Windows build, but if it works...

[mtklein_C, 2016/11/18 21:03:56]

Yeah.  It's the only way to express things like -mssse3 and -msse4.1, so we do
this for consistency.

       }
       if (is_win) {
-        cflags = [ "/arch:AVX" ]
+        defines = [ "SK_CPU_SSE_LEVEL=51" ]
       }
       visibility = [ ":skia_opts" ]
       configs -= [ "//build/config/compiler:chromium_code" ]
@@ -566,7 +569,7 @@ if (!skia_build_no_opts) {
     }
     source_set("skia_opts_hsw") {
       sources = skia_opts.hsw_sources
-      if (!is_win) {
+      if (!is_win || is_clang) {

[brucedawson, 2016/11/18 21:00:26]

This may have unintended consequences because now four previously unused flags
are being passed to clang-cl.

[mtklein_C, 2016/11/18 21:03:56]

Hmm.  I think it should be okay, especially because it's restricted to only
clang-cl.  We've been using these flags with clang-not-cl for a while now.

         cflags = [
           "-mavx2",
           "-mbmi",
@@ -576,7 +579,7 @@ if (!skia_build_no_opts) {
         ]
       }
       if (is_win) {
-        cflags = [ "/arch:AVX2" ]
+        defines = [ "SK_CPU_SSE_LEVEL=52" ]
       }
       visibility = [ ":skia_opts" ]
       configs -= [ "//build/config/compiler:chromium_code" ]