Auto merge of #878 - servo:jdm-patch-22, r=Manishearth

Add arm platform builders.

This would be useful for ajeffrey's work.

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homu/map.jinja

@@ -7,7 +7,8 @@
         'mac': ['mac-dev-unit'],
         'windows': ['windows-msvc-dev'],
         'wpt': ['linux-rel-css', 'linux-rel-wpt'],
-        'android': ['android', 'android-x86']
+        'android': ['android', 'android-x86'],
+        'arm': ['arm32', 'arm64']
     }
   }
 %}