I agree it's not very relevant in this case, but I have measured this 
adding Swift to an otherwise-empty (just sleep()s in main) C process on my Darwin system adds 128kB of total dirty memory, of which 16kB is heap memory coming from 28 additional allocations.
This will vary depending on system libraries, symbol ordering, memory allocator, and other factors of course. My particular system is likely measuring a bit on the high side at the moment for unrelated reasons.
(edited to correct numbers slightly, I forgot I had edited my test program, and reverting the edits reduced it from 176kB to 128kB and from 37 allocations to 28)