[CMake] Modern CMake + CUDA + Clang

[Stephen McDowell]

Excellent, this is very useful — thanks Robert!

I think I have some answers to some of these, but as I make progress will probably reach out to the LLVM mailing lists for help / suggestions (particularly with separable compilation and device linking).

I’m still ramping up to speed on developing CMake.  You had mentioned CMake_TEST_CUDA which will be helpful down the line, but intermediately is it “ok” to just modify *.cmake modules in-place underneath the installed Modules and Modules/Compiler directories?  I’ve got a custom install / am not concerned about breaking things in it, I’m just wondering if this is a typical practice or if I should be re-compiling and re-installing every time I make changes.