V8: Get build environment from MB

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___nosnap_builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.v8",
       "--builder",
       "V8 Linux - nosnap builder",
@@ skipping 359 matching lines @@
     "name": "package build"
   },
   {
     "cmd": [],
     "name": "trigger",
     "trigger_specs": [
       {
         "builder_name": "V8 Linux - nosnap",
         "properties": {
           "parent_build_environment": {
-            "GYP_DEFINES": "target_arch=ia32 test_isolation_mode=prepare use_goma=1 v8_target_arch=ia32 v8_use_snapshot=false",
-            "GYP_GENERATORS": "ninja"
+            "GYP_DEFINES": "target_arch=x64 cool_flag=a=1"
           },
           "parent_got_revision": "f2cbea7e89a45f46819777bb78a1f5bd0241f64c",
           "parent_got_revision_cp": "refs/heads/master@{#50110}",
           "parent_got_swarming_client_revision": "e4fee0b18f8163be6097c9c571640038896debc4",
           "revision": "f2cbea7e89a45f46819777bb78a1f5bd0241f64c",
           "swarm_hashes": {
             "bot_default": "[dummy hash for bot_default]",
             "mozilla": "[dummy hash for mozilla]",
             "simdjs": "[dummy hash for simdjs]",
             "test262": "[dummy hash for test262]"
           }
         }
       }
     ],
     "~followup_annotations": [
       "@@@STEP_TEXT@V8 Linux - nosnap@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]