Rewrite the corehost CMake system to be more "Modern CMake"y and less MSBuild-y

[jkoritzinsky]

• Use configure_file instead of stringly-defined macros.
• Flow include directories through CMake target definitions.
• Use functions instead of include(foo.cmake)

This moves our CMake for the hosts build to be more similar to the rest of the build and more similar to CMake documentation you'll find online. This also removes quite a bit of duplicate/unnecessary CMake for some targets that was applied more widely than necessary.

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