I've posted multiple times about this on the forums before (Error starting the swift repl on windows - #5 by compnerd), please search first. Reporting errors should go through the Swift bug tracking system, not the forums nor LLVM's issues.
While the REPL works (particularly when cajoled to do the right thing), it doesn't work out of the box due to some regression that has crept in a long while back in LLDB. You're welcome to investigate and fix that, there are some pointers for what is going on at Can't interpret .swift file on Windows - #7 by compnerd. I've done some work to improve the lldb implementation for library loading, but that still doesn't handle the library search paths properly. This might be best fixed in the Swift local lldb changes.
In the mean time, I recommend that you just compile the code instead of executing it in the REPL.