Apply CI compiler warning flags in CMake

[cwpearson]

This makes the warning flags we use in CI directly accessible in development with -DKokkosKernels_ENABLE_COMPILER_WARNINGS=ON

[cwpearson]

Thoughts on this general approach @e10harvey @lucbv?

[e10harvey]

Thoughts on this general approach @e10harvey @lucbv?

This approach looks reasonable to me. FWIW, this is a similar divergence that was used in trilinos (branching in both shell and cmake scripts for different systems and compilers) that led to significant complexity and maintainability challenges. cm_test_all_sandia has kept this branching and complexity mostly within the script itself, which, in my opinion, has worked very well.

These configuration use-cases are exactly what GenConfig was designed to address. I do not think this PR introduces significant complexity and maintainability challenges. If managing this configuration infrastructure becomes a pain point, please consider addressing it.

[cwpearson]

Converting this to an issue to possibly revisit later.