[CMake] Deprecate build.sh

[ppenzin]

build.sh has always been purely a wrapper around CMake. After community transition we have added a 'bare' CMake workflow that doesn't use it and now using that exclusively in CI. The script seems to only convert its non-sticky --option's to CMake's normally-sticky -DOPTION's, which requires additional logic in the main CMakeLists.txt.

We should also try to inventory what other options build.sh has and try to port them back to regular CMake if they are useful. I've recently found ccache which went into #7053.

This is low priority and shouldn't go to the release branch.

#1616 is also talking about improving CMake support.