Yeah, that's cause compiling uses 100% of your CPU if it can, compiling is a pretty intensive process and takes time. Just be patient, it hasn't crashed it's just working its way through.
If it freezes for over an hour you've probably got issues with optimization.
Likely problems are intricate detail that isn't func_detail, portalflow is where a lot of new mappers have problems. If you're not very sensible about your geometry portalflow can reach multiple hours. If however you aren't too messy it can take as little as 10 seconds or less (how it should be)
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