Includes functions offered by Windows that are similar in
spirit to mmap.
Currently these are low-level FFI versions only, and no attempt
is made to export them from sb-posix under the name mmap. In
sb-posix, only a wrapper for msync and definitions of several
constants is offered, as needed for sb-simple-streams.
Thanks to Anton Kovalenko.
Also take this opportunity to sort the sb-win32 package
definition as a flat list.