Bug 1527777 - Apply change to Windows jobs too r=jmaher

Differential Revision: https://phabricator.services.mozilla.com/D21299

--HG--
extra : moz-landing-system : lando

taskcluster/taskgraph/transforms/job/spidermonkey.py

@@ -106,6 +106,8 @@ def generic_worker_spidermonkey(config, job, taskdesc):
         'SRCDIR': "./src",  # with values suiteable for windows generic worker
         'UPLOAD_DIR': "./public/build"
     })
+    if 'spidermonkey-platform' in run:
+        env['SPIDERMONKEY_PLATFORM'] = run['spidermonkey-platform']
 
     script = "build-sm.sh"
     if run['using'] == 'spidermonkey-package':