Enable libnativehelper for Windows

This requires using the Windows specific API for loading/manipulating
native libraries, and string printing.
libnativehelper is a dependency of layoutlib native (used for desktop
rendering of Android resources), which is why it needs a Windows verion.

Bug: 117921091
Test: lunch sdk && make libnativehelper
Change-Id: I20fa392ac7e3c031ce076435bf4380205992608b