Stand-alone builds need an installed version of gtest in order to run
the unittests.
Reviewed By: mgorny, kwk
Differential Revision: https://reviews.llvm.org/D137890
The Annotations helper class does not have a gtest or gmock dependency, but because it's bundled with the rest of TestingSupport, it gets one. By splitting it out, a target can use it without being forced to use LLVM's copy of gtest.
Reviewed By: GMNGeoffrey, sammccall, gribozavr2
Differential Revision: https://reviews.llvm.org/D141175