Fix BUILD.gn for arch other then x86 and x64

opts_gypi should only be defined for x86 and x64 else we get unused
variable error

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248323002

Review-Url: https://codereview.chromium.org/2248323002
diff --git a/BUILD.gn b/BUILD.gn
index b18cdd4..1c1cfec 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -144,6 +144,11 @@
                          "scope",
                          [ "gyp/utils.gypi" ])
 
+source_set("opts_none") {
+  configs += skia_library_configs
+  sources = opts_gypi.none_sources
+}
+
 is_x86 = current_cpu == "x64" || current_cpu == "x86"
 
 if (is_x86) {
@@ -199,6 +204,8 @@
       ":opts_sse42",
       ":opts_ssse3",
     ]
+  } else {
+    deps += [ ":opts_none" ]
   }
 
   if (!is_win) {
@@ -530,8 +537,8 @@
   sources = [
     "experimental/svg/model/SkSVGAttribute.cpp",
     "experimental/svg/model/SkSVGAttributeParser.cpp",
-    "experimental/svg/model/SkSVGContainer.cpp",
     "experimental/svg/model/SkSVGCircle.cpp",
+    "experimental/svg/model/SkSVGContainer.cpp",
     "experimental/svg/model/SkSVGDOM.cpp",
     "experimental/svg/model/SkSVGEllipse.cpp",
     "experimental/svg/model/SkSVGLine.cpp",