Allow building emulator as an sdk-addon

This can be imported into Android Studio more easily, eventually even
as a repository of LineageOS emulator images.

(Build with `m sdk_addon`, it will end up in out/host/linux-x86/sdk_addon)

Change-Id: Ia78524dd729b0f2ccc96f5a6eb2503cdc8b4d253
2 files changed