android_build/target/board/generic_64bitonly_x86_64
..
BoardConfig.mk
README.txt
device.mk
system.prop

README.txt

The "generic_x86_64_app" product defines a non-hardware-specific IA target
without a kernel or bootloader.

It can be used to build the entire user-level system, and
will work with the IA version of the emulator,

This supports 64-bit apps only.