WebRTC: Add Linux GCC bot.

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_linux64_gcc.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "client.webrtc.fyi",
       "--builder",
-      "Linux32 ARM",
+      "Linux64 GCC",
       "--slave",
       "slavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/external/webrtc'}, {'deps_file': 'DEPS', 'managed': True, 'name': 'webrtc-limited', 'url': 'https://chrome-internal.googlesource.com/chrome/deps/webrtc-limited'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{\"src\": \"got_revision\"}",
       "--output_json",
       "/path/to/tmp/json",
@@ skipping 48 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
-      "GYP_CROSSCOMPILE": "1",
-      "GYP_DEFINES": "component=static_library dcheck_always_on=1 gomadir='[BUILD]/goma' target_arch=arm use_goma=1"
+      "GYP_DEFINES": "clang=0 component=static_library gomadir='[BUILD]/goma' target_arch=x64 use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
       "--target",
       "Release",
@@ skipping 11 matching lines @@
       "All"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   }
 ]