Move the test setup to the general test setup.
Tests: Build alt-test-generator tests in a separate binary dir.

This way, a single CMake build tree can be used to run the
unit tests with multiple generators.
Merge topic 'alt-test-generator' into next

7f91eb83 Tests: Build alt-test-generator tests in a separate binary dir.
adb89ea3 Move the test setup to the general test setup.