Re-enable BUILD_TESTS for fbcode_builder
Re-enable BUILD_TESTS for fbcode_builder

Summary: As it turns out, several of the `fizz` dependencies require it to have been built with tests enabled, so it's just easier to build them always, IIRC they only waste 1-2 minutes of time.

Reviewed By: lnicco

Differential Revision: D17837758

fbshipit-source-id: dd0c73b3aaf72831ce702dbcecd4e3ff627a4901

facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman