Add SSE4 optimization of S32A_Opaque_Blitrow

src/opts/SkBlitRow_opts_SSE4.h

Index: src/opts/SkBlitRow_opts_SSE4.h
diff --git a/src/opts/SkBlitRow_opts_SSE4.h b/src/opts/SkBlitRow_opts_SSE4.h
new file mode 100644
index 0000000000000000000000000000000000000000..b34dbf0594a7544c6baf90f851e190d41e6cd0a0
--- /dev/null
+++ b/src/opts/SkBlitRow_opts_SSE4.h
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2013 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"
+
+#if defined(__clang__) || (defined(__GNUC__) && !defined(SK_BUILD_FOR_MAC))

[mtklein, 2014/06/17 15:14:29]

So, help me parse this condition now?

  Clang -> Yes
  GCC   -> Yes, unless on Mac

Meaning, we'll build for Mac with Clang, Linux with Clang or GCC, Android with
Clang or GCC, and not at all for Windows.  Is that right?  If so, SGTM.  

Can you just tack on a reminder comment that the GCC-on-Mac check is to guard
against LLVM-GCC 4.2?  Presumably vanilla GCC on Mac would work fine, but that's
not really a viable choice anymore anyway.

Maybe define SK_SSE4_ASM_SUPPORTED when this is true so that the other places
that use this same condition can have something a bit more semantic to check?

[henrik.smiding, 2014/06/17 18:16:38]

Correct.
Added a flag and updated the two checks in opts_check file.

+extern "C" void S32A_Opaque_BlitRow32_SSE4_asm(SkPMColor* SK_RESTRICT dst,
+                                               const SkPMColor* SK_RESTRICT src,
+                                               int count, U8CPU alpha);
+#endif
+
+#endif
+