libyuv: Add GCC trybot.

scripts/slave/recipes/libyuv/libyuv.expected/tryserver_libyuv_linux_gcc.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "tryserver.libyuv",
       "--builder",
-      "linux_rel",
+      "linux_gcc",
       "--slave",
       "slavename",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_vars': {'root_dir': 'src'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/libyuv/libyuv'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{}",
       "--git-cache-dir",
       "[GIT_CACHE]",
@@ skipping 30 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]/src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
-      "GYP_DEFINES": "component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' target_arch=x64 use_goma=1",
+      "GYP_DEFINES": "clang=0 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' target_arch=x64 use_goma=1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py",
       "--show-path",
@@ skipping 35 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
       "--target",
       "Release",
       "--no-xvfb",
       "--factory-properties",
-      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_rel\", \"mastername\": \"tryserver.libyuv\", \"patch_url\": \"try_job_svn_patch\", \"recipe\": \"libyuv/libyuv\", \"revision\": \"12345\", \"slavename\": \"slavename\"}",
+      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_gcc\", \"mastername\": \"tryserver.libyuv\", \"patch_url\": \"try_job_svn_patch\", \"recipe\": \"libyuv/libyuv\", \"revision\": \"12345\", \"slavename\": \"slavename\"}",
       "--build-properties",
-      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_rel\", \"mastername\": \"tryserver.libyuv\", \"patch_url\": \"try_job_svn_patch\", \"recipe\": \"libyuv/libyuv\", \"revision\": \"12345\", \"slavename\": \"slavename\"}",
+      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_gcc\", \"mastername\": \"tryserver.libyuv\", \"patch_url\": \"try_job_svn_patch\", \"recipe\": \"libyuv/libyuv\", \"revision\": \"12345\", \"slavename\": \"slavename\"}",
       "--step-name=libyuv_unittest",
-      "--builder-name=linux_rel",
+      "--builder-name=linux_gcc",
       "--slave-name=slavename",
       "libyuv_unittest"
     ],
     "name": "libyuv_unittest"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]