Concurrency is possible on a single core, since concurrency and multi-threading are orthogonal. You can have truly concurrent code running on a single core with event loops (cooperative concurrency) or threads (preemptive concurrency), which is exactly how it worked before multiple cores became widely available on consumer hardware.
I don't think that performance itself is related to async/await per se in the single-threaded environment. The main question is whether the code you write is blocking or non-blocking.
If your code is non-blocking, you probably already use either callbacks or async/await, and I think there's a general consensus that async/await is easier to maintain than callbacks, especially in terms of error handling.
If your code is blocking and I/O-bound, then probably switching to async/await is easier than switching to callbacks. If your code is CPU-bound, then on a single core suspension points will likely add some overhead, but there unlikely to be a performance benefit.
Of course, I don't know the details of what you write, YMMV. Parts of your application can be I/O-bound and other parts CPU-bound, then using async/await for the former makes sense, but not for the latter.
I'd recommend cross-compiling if possible, we have a proposal in review that could help with that.