Skia: Supply --gcc to android_ninja when appropriate

scripts/slave/recipes/skia/swarm_compile.expected/Build-Ubuntu-GCC-Arm7-Release-Android.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/skia/tools/buildbot_spec.py",
       "/path/to/tmp/json",
       "Build-Ubuntu-GCC-Arm7-Release-Android"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 63 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  pass@@@",
       "@@@STEP_LOG_LINE@python.inline@print json.dumps({'ccache': ccache})@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "[SLAVE_BUILD]/skia/platform_tools/android/bin/android_ninja",
       "dm",
       "-d",
-      "arm_v7_neon"
+      "arm_v7_neon",
+      "--gcc"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
     "env": {
       "ANDROID_HOME": "/b/android-sdk-linux",
       "ANDROID_SDK_ROOT": "/b/android-sdk-linux",
       "BUILDTYPE": "Release",
       "CHROME_HEADLESS": "1",
       "GYP_DEFINES": "skia_arch_type=arm skia_warnings_as_errors=1",
       "PATH": "[SLAVE_BUILD]/depot_tools:%(PATH)s",
       "SKIA_ANDROID_VERBOSE_SETUP": "1",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "build dm"
   },
   {
     "cmd": [
       "[SLAVE_BUILD]/skia/platform_tools/android/bin/android_ninja",
       "nanobench",
       "-d",
-      "arm_v7_neon"
+      "arm_v7_neon",
+      "--gcc"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
     "env": {
       "ANDROID_HOME": "/b/android-sdk-linux",
       "ANDROID_SDK_ROOT": "/b/android-sdk-linux",
       "BUILDTYPE": "Release",
       "CHROME_HEADLESS": "1",
       "GYP_DEFINES": "skia_arch_type=arm skia_warnings_as_errors=1",
       "PATH": "[SLAVE_BUILD]/depot_tools:%(PATH)s",
       "SKIA_ANDROID_VERBOSE_SETUP": "1",
@@ skipping 35 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@    shutil.move(f, dst)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]