GN: support 32-bit x86 builds

BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("gn/shared_sources.gni")
 
 declare_args() {
   skia_enable_tools = !is_fuchsia && !is_component_build
 
@@ skipping 536 matching lines @@
 
 action("skia.h") {
   script = "gn/echo_headers.py"
   args = [ rebase_path("$target_gen_dir/skia.h", root_build_dir) ] +
          rebase_path(skia_h_headers, target_gen_dir)
   outputs = [
     "$target_gen_dir/skia.h",
   ]
 }
 
-executable("fiddle") {
-  include_dirs = [ "$target_gen_dir" ]
-  libs = []
-  if (is_linux) {
-    libs += [ "OSMesa" ]
+if (target_cpu == "x64") {
+  # Our bots only have 64-bit libOSMesa installed.
+  # TODO: worth fixing?
+  executable("fiddle") {
+    include_dirs = [ "$target_gen_dir" ]
+    libs = []
+    if (is_linux) {
+      libs += [ "OSMesa" ]
+    }
+
+    sources = [
+      "src/images/SkForceLinking.cpp",
+      "tools/fiddle/draw.cpp",
+      "tools/fiddle/fiddle_main.cpp",
+    ]
+    deps = [
+      ":skia",
+      ":skia.h",
+    ]
   }
-
-  sources = [
-    "src/images/SkForceLinking.cpp",
-    "tools/fiddle/draw.cpp",
-    "tools/fiddle/fiddle_main.cpp",
-  ]
-  deps = [
-    ":skia",
-    ":skia.h",
-  ]
 }
 
 # Targets guarded by skia_enable_tools may use //third_party freely.
 if (skia_enable_tools) {
   template("test_lib") {
     config(target_name + "_config") {
       include_dirs = invoker.public_include_dirs
     }
     source_set(target_name) {
       forward_variables_from(invoker, "*", [ "public_include_dirs" ])
@@ skipping 252 matching lines @@
     sources = [
       "tools/SkShaper_primitive.cpp",
       "tools/using_skia_and_harfbuzz.cpp",
     ]
     deps = [
       ":skia",
     ]
     testonly = true
   }
 }