(Updated Dec 2017)

Here's how I'm building CrossWords for Android.

First, cd into the directory xwords4/android. Everything
happens there.

To build and install the debug version of CrossWords:

# ./gradlew clean insXw4Deb

To build and install the debug version of CrossDbg (a variant meant
for development that can co-exist with CrossWords):

# ./gradlew -PuseCrashlytics insXw4dDeb

I do all development on Debian and Ubuntu Linux systems. I have built
on MacOS, where once you get all the necessary tools installed via
homebrew there's only one problem I'm aware of: the parameter 'white'
that's passed to convert by android/scripts/images.mk on Linux systems
needs to be 'black' on MacOS. I have no clue why. If you don't make
this change the subset of actionbar icons that are generated from .svg
files will be black-on-black.