Replace reduce(operator.or_, ...) with any(...).

The any() builtin was introduced in Python 2.5. Not only is its intent
clearer, but it handles the case of zero items -- which the reduce(or_)
construct does not. Sporadically we've seen exceptions from
generate_breakpad_symbols.py when reduce(or_, ...) is given zero items. This
masks the actual error (failure to dump symbols? failure to read them?),
masquerading as a bug in the Python script.