Attempt to let skia's SSE files build with clang-cl.

cl.exe can use intrinsics (like e.g. _mm_cvtsi128_si32()) even if arch
targetted by the compiler doesn't support the SSE level needed by the intrinsic.

clang (and gcc) can't do this, because it converts intrinsics into general
LLVM operations, and the LLVM bitcode is then translated back into assembly
later on, based on the target arch.

So explicitly enable SSSE3 and SSE4 when using clang-cl, so that the intrinsics
compile.

(It's unfortunate that clang-cl deviates fairly heavily from cl in this regard.
But this is very difficult to change, and it's the only larger deviation so
far.)

BUG=82385
R=rnk@chromium.org

Review URL: https://codereview.chromium.org/475273002

Cr-Commit-Position: refs/heads/master@{#289735}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289735 0039d316-1c4b-4281-b951-d872f2087c98

skia/skia_library_opts.gyp

@@ -177,6 +177,13 @@
             'GCC_ENABLE_SUPPLEMENTAL_SSE3_INSTRUCTIONS': 'YES',
           },
         }],
+        [ 'OS == "win" and clang == 1', {
+          # cl.exe's /arch flag doesn't have a setting for SSSE3, and cl.exe
+          # doesn't need it for intrinsics. clang-cl does need it, though.
+          'msvs_settings': {
+            'VCCLCompilerTool': { 'AdditionalOptions': [ '-mssse3' ] },
+          },
+        }],
         [ 'OS == "win"', {
           'include_dirs': [
             'config/win',
@@ -226,6 +233,13 @@
             'GCC_ENABLE_SSE41_EXTENSIONS': 'YES',
           },
         }],
+        [ 'OS == "win" and clang == 1', {
+          # cl.exe's /arch flag doesn't have a setting for SSE4.1, and cl.exe
+          # doesn't need it for intrinsics. clang-cl does need it, though.
+          'msvs_settings': {
+            'VCCLCompilerTool': { 'AdditionalOptions': [ '-msse4.1' ] },
+          },
+        }],
         [ 'OS == "win"', {
           'defines' : [
             'SK_CPU_SSE_LEVEL=41'