Bug 1580280 - [configure] Define '__bool__' on PositiveOptionValue for Python 3 compatibility, r=nalexander

Differential Revision: https://phabricator.services.mozilla.com/D47609

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

python/mozbuild/mozbuild/configure/options.py

@@ -107,7 +107,10 @@ class PositiveOptionValue(OptionValue):
     --option=value[,value2...].
     '''
 
-    def __nonzero__(self):
+    def __nonzero__(self):  # py2
+        return True
+
+    def __bool__(self):  # py3
         return True