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ARROW-3441: [Gandiva] Use common unit test creation facilities, do not produce multiple executables for the same unit tests

This also adds a "gandiva" CMake target so you can run `ninja gandiva`. Additionally, all unit tests now have a `gandiva-` prefix.

Author: Wes McKinney <wesm+git@apache.org>

Closes #3091 from wesm/ARROW-3441 and squashes the following commits:

d6f4703de <Wes McKinney> Add option to ADD_ARROW_TESTS to override global NO_TESTS option
4f006feb3 <Wes McKinney> Add prefix for precompiled tests, add to gandiva target
5bdfd3090 <Wes McKinney> Add ADD_GANDIVA_TEST function, remove GandivaBuildUtils, cleaning. Add gandiva custom target