[CMake] Unity builds (was: Re: [ANNOUNCE] CMake 3.16.0-rc1 is ready for testing)

[Paul Smith]

On Thu, 2019-10-10 at 14:57 -0400, Robert Maynard via CMake wrote:
> * The "UNITY_BUILD" target property was added to tell generators to
>   batch include source files for faster compilation times.

Are there any instructions on how to make this work?  I tried this:

  cmake -G 'Unix Makefiles' -DCMAKE_UNITY_BUILD=ON .

Then ran "make".  The output showed I had just as many output .o files
as input .cpp files and that make ran one compile command per .cpp
file.

Is there something else I need to do to enable unity builds in my cmake
files, than just give the above option?  The docs imply that the above
is all that's needed.

Cheers!