cygwin has also a nasty bug:
    printf("%ls", wide_string)
fails for strings of length 1. %S has the same problem.

$ ./python.exe ab
./python: can't open file 'ab': [Errno 2] No such file or directory

$ ./python.exe a
./python

The output stops at "./python", probably because stderr has an error
flag set.

Since %ls is only used in Modules/main.c, the best is probably to
replace it with something else. And since cygwin has no function of the
family of wprintf or fputws, PyUnicode is probably the way to go.