Lay groundwork for SkOpts.

This doesn't really do anything yet.  It's just the CPU detection code, skeleton new .cpp files, and a few little .gyp tweaks.

BUG=skia:4117

Committed: https://skia.googlesource.com/skia/+/ce2c5055cee5d5d3c9fc84c1b3eeed4b4d84a827

Review URL: https://codereview.chromium.org/1255193002
diff --git a/gyp/opts.gypi b/gyp/opts.gypi
index 6d7a796..44e57d52 100644
--- a/gyp/opts.gypi
+++ b/gyp/opts.gypi
@@ -34,6 +34,7 @@
             '<(skia_src_path)/opts/SkTextureCompression_opts_neon.cpp',
             '<(skia_src_path)/opts/SkUtils_opts_arm_neon.cpp',
             '<(skia_src_path)/opts/SkXfermode_opts_arm_neon.cpp',
+            '<(skia_src_path)/opts/SkOpts_neon.cpp',
         ],
         'arm64_sources': [
             '<(skia_src_path)/opts/SkBitmapProcState_arm_neon.cpp',
@@ -51,6 +52,7 @@
             '<(skia_src_path)/opts/SkUtils_opts_none.cpp',
             '<(skia_src_path)/opts/SkXfermode_opts_arm.cpp',
             '<(skia_src_path)/opts/SkXfermode_opts_arm_neon.cpp',
+            '<(skia_src_path)/opts/SkOpts_neon.cpp',
         ],
 
         'mips_dsp_sources': [
@@ -74,12 +76,15 @@
             '<(skia_src_path)/opts/SkUtils_opts_SSE2.cpp',
             '<(skia_src_path)/opts/SkXfermode_opts_none.cpp',
             '<(skia_src_path)/opts/opts_check_x86.cpp',
+            '<(skia_src_path)/opts/SkOpts_sse2.cpp',
         ],
         'ssse3_sources': [
             '<(skia_src_path)/opts/SkBitmapProcState_opts_SSSE3.cpp',
+            '<(skia_src_path)/opts/SkOpts_ssse3.cpp',
         ],
         'sse41_sources': [
             '<(skia_src_path)/opts/SkBlurImage_opts_SSE4.cpp',
             '<(skia_src_path)/opts/SkBlitRow_opts_SSE4.cpp',
+            '<(skia_src_path)/opts/SkOpts_sse41.cpp',
         ],
 }