osx sdk location and android fixes

* Reverts to the original way of setting sdk location, but uses xcode-select to get the real xcode location, instead of hardcoding something.
* In case the sdks aren't in the xcode path, use /Developer/SDKs (hardcoded)
(we could add a test to at least see if it exists and fail if it doesn't)

* I also added some stuff that was missing for android post-build