Support CMake 3.16 UNITY_BUILD
I assume VTK built time can be reduced significantly using CMake 3.16 unity build support:
To get to a point where using
cmake -DCMAKE_UNITY_BUILD=ON works we need 2 things:
- Disable the UNITY_BUILD property of third-party dependencies targets (I tried, the build fails here first)
- Blacklist sources files that should be excluded from unity builds with the source file property SKIP_UNITY_BUILD_INCLUSION (static variables conflict, conflicting headers...)
what do you think @ben.boeckel ?