CMake: always build tests by default on UNIX || APPLE
CMake: always build tests by default on UNIX || APPLE

Now that googletest can be fetched.

darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed