Depending on your definition of a standard library module there could be a few lists. For example, _Concurrency is technically a stdlib module, it's just implicitly imported for you. There are also some C modules that are exposed as importable Swift modules like Darwin, Glibc, etc. That said, these are all of the Swift/C modules that exist in the standard library:
I believe that's all of them (or at least most of the them, there are a couple of others I didn't include just because they aren't usable outside of the stdlib etc.)