Exclude Clang on Windows too. Comment this up a bit.

src/opts/SkBlitRow_opts_SSE4.h

 /*
  * Copyright 2014 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBlitRow_opts_SSE4_DEFINED
 #define SkBlitRow_opts_SSE4_DEFINED
 
 #include "SkBlitRow.h"
 
-/* Check if we are able to build assembly code, GCC/AT&T syntax.
- * Had problems with LLVM-GCC 4.2.
- * MemorySanitizer cannot handle assembly code.
+/* Check if we are able to build assembly code, GCC/AT&T syntax:
+ *  1) Clang and GCC are generally OK.  OS X's old LLVM-GCC 4.2 can't handle it;

[Nico, 2014/07/02 19:05:46]

(fwiw, we don't use OS X's llvm-gcc in chrome. Maybe you care about it for skia
for other reasons though.)

+ *  2) Clang for Windows doesn't support AT&T syntax;

[Reid Kleckner, 2014/07/02 19:04:48]

This comment isn't true, Clang can probably assemble that .s file.  It's just
that gyp isn't asking it to.  Wiring that up isn't high priority, given that
clang for windows is in pretty early days, but eventually we could do it.

[Nico, 2014/07/02 19:05:46]

I think it does – the problem on the bug is just that the .S file doesn't get
compiled on Windows, and maybe gyp doesn't build .S files on Windows. But I
think clang/win does support both syntaxes:

D:\src\hack\watdbg>..\..\llvm-ninja\bin\clang -c test.cc

D:\src\hack\watdbg>type test.cc
int main() {
      int a=10, b;
        asm ("movl %1, %%eax; movl %%eax, %0;"
             :"=r"(b)        /* output */
             :"r"(a)         /* input */
             :"%eax"         /* clobbered register */
             );

}

+ *  3) MemorySanitizer cannot instrument assembly at all.
  */
-#if (defined(__clang__) || (defined(__GNUC__) && !defined(SK_BUILD_FOR_MAC))) \
-    && !defined(MEMORY_SANITIZER)
+#if /* 1)*/ (defined(__clang__) || (defined(__GNUC__) && !defined(SK_BUILD_FOR_MAC))) \
+    /* 2)*/ && !defined(SK_BUILD_FOR_WIN)                                             \
+    /* 3)*/ && !defined(MEMORY_SANITIZER)
 extern "C" void S32A_Opaque_BlitRow32_SSE4_asm(SkPMColor* SK_RESTRICT dst,
                                                const SkPMColor* SK_RESTRICT src,
                                                int count, U8CPU alpha);
 
 #define SK_ATT_ASM_SUPPORTED
 #endif
 
 #endif