Here is my BrE contribution, for what it's worth - if anything.
I would not go as far as labelling 'before' archaic, but it is pretty formal, In normal conversation it wold be very unusual with buildings, and sometimes wrong/confusing - see SoothingDave's post #7.
I think part of the problem started with engee's first response, "Such use is considered formal by some. And of course it's correct." In the original sentence, There was a large crowd before/in front of the City Hall, 'before' is not really formal; it is unnatural; in that particular sentence I would go so far as to say it is not 'correct'.
Yes, if we are formal, we stand before a judge, a Senate committee, an audience, a congregation, etc, but we do NOT park our car before our house, and crowds do not normally stand before City Hall.
Dictionaries, rightly, list this meanng of 'before' because, in the past, it was used with places meaning 'in front of'; indeed it may well still be used in this way by some writers. Advanced students should certainly be made aware of this.
However, to suggest to most learners that 'before' is correct or natural in the original sentence is unhelpful.
if you look back through the thread, you will not find one native speaker who feels that it is natural in normal modern English.