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

[Kyle Edwards]

On Fri, Oct 11, 2019 at 1:36 AM Alan W. Irwin
<Alan.W.Irwin1234 at gmail.com> wrote:
> The source files that have COMPILE_OPTIONS, COMPILE_DEFINITIONS, COMPILE_FLAGS, or INCLUDE_DIRECTORIES will also be skipped."

This is by far the most likely reason. We added this restriction
because we don't want files that have different COMPILE_FLAGS etc. to
be lumped together in a unity file. We decided that this was good
enough as a first past, but the way forward is to intelligently group
together files that have the same COMPILE_OPTIONS,
COMPILE_DEFINITIONS, COMPILE_FLAGS, and INCLUDE_DIRECTORIES.

Kyle