The (originally called) DeepScreen scan is done on files rarely seen on our userbase... so that's exactly what the newly compiled executables would be.
So I think excluding the output folder is the way to go. (Of course, ideally it would only be excluded for DeepScreen/AutoSandbox, not for regular scanning - which I think the program still supports, but unfortunately that setting is completely gone from the UI).
As for detecting the "developer" scenario automatically... we discussed it a few times in the past, but:
1. There are many possible cases (development tools, compilers)
2. It could probably be abused - a malicious downloader somehow pretending to be a compiler (by whatever features we'd be detecting it, even if it meant including the original compiler binary and changing its behavior by launching a custom thread within the process) and avoiding the scan that way