Android classpath support in Windows

This pull request is connected to the other one made in android-libcore64 repo: https://github.com/dicej/android-libcore64/pull/1 (it will make sense only if Joel accepts the other one)

Together they make Avian + Android classpath useful on Windows.

The work on porting is incomplete, but some goals have already been achieved:
* Sockets work (even in some tough situations)
* Simple I/O works
* Many other Java-only classes in the default library should work out-of-the-box cause they are not connected to POSIX functions

This pull request is linked to the issue https://github.com/ReadyTalk/avian/issues/168