[CMake] [proposal] Support for modern CMake

[Brad King]

On 03/22/2018 10:17 AM, Mateusz Loskot wrote:
> It seems folks generally agree there is need for porcelain API.
> It's a pity it's been 5+ years and it is still waiting for implementation.

For reference, there were several discussions.  Some of them were here:

* "Setting include directories via target_link_libraries"
  https://cmake.org/pipermail/cmake-developers/2012-December/017561.html

* "Setting includes, defines and other usage requirements with one command"
  https://cmake.org/pipermail/cmake-developers/2013-January/017939.html

It was an extended debate over whether a separate `target_use_targets`
command should be introduced instead of propagating usage requirements
through `target_link_libraries`.  The main driving factor was compatibility
with existing projects using `target_link_libraries` at the time.

In the end it was decided that the extra command would be redundant and
we proceeded with `tll()` only.  I'd prefer not to have this debated
endlessly again.

Perhaps the name `target_link_libraries` no longer fully conveys the
semantics, but it's good enough and has worked well for years now.

-Brad