[C] Add support for CMake package

[kou]

fix #89

[lidavidm]

Thanks!

As you can see, the CMake config is mostly copy-pasted from Arrow - I wonder if you have general thoughts about continuing to do this, or trying to build up the CMake config from first principles (like nanoarrow did)

[kou]

I think that "trying to build up the CMake config from first principles" is better for maintainability. I think that ADBC can be built with simple build config. (Arrow needs complex build config because it has many components, depends on many libraries and so on...)
Arrow's common CMake modules have some helpful features but it's complex. We'll refactor Arrow's CMake modules in the future Arrow development. Backporting changes from Arrow to ADBC may be difficult.

FYI: The changes for BuildUtils.cmake in this pull request is backported from apache/arrow#13892 .

[lidavidm]

Makes sense - I filed #92.