Opensource Buck2 build

[PhilipMetzger]

Could you opensource the buck2 build files (TARGETS, BUCK)? I've recently have become interested in HHVM and as the CMake build is community supported, providing the internally supported build would be nice. That would enable a part of the community to build from source at HEAD.

[haowanaa]

您好，来信我已收到，我将尽快给您回复。

[lexidor]

I have added build and wishlist to this GH Issue. I'd appreciate if this came to pass, but I have no idea how feasible this would be.