Bug 1439258: Set SCCACHE controlling environment variables on windows workers; r=dustin

Since comm-central doesn't have integration branches like autoland, we want to
always disable sccache on nightly builds, rather than being able to key off of
the tree to determine whether to enable it. This is currently done by not
including the sccache toolchain. However, the mozconfig files expect sccache to be
available if `SCCACHE_DISABLE` isn't set, which wasn't the case on windows.

Differential Revision: https://phabricator.services.mozilla.com/D603

--HG--
extra : rebase_source : 565d0b6a3b24a23f6ae844a8cd97b9824e9f5282
extra : amend_source : 8c1679a71a2baf04a0dc83074234c5101705b806

taskcluster/taskgraph/transforms/task.py

@@ -962,7 +962,10 @@ def build_generic_worker_payload(config, task, task_def):
         'osGroups': worker.get('os-groups', []),
     }
 
-    # needs-sccache is handled in mozharness_on_windows
+    if task.get('needs-sccache'):
+        worker['env']['USE_SCCACHE'] = '1'
+    else:
+        worker['env']['SCCACHE_DISABLE'] = '1'
 
     # currently only support one feature (chain of trust) but this will likely grow
     features = {}