Issue Description:

The "overlay" libraries in stdlib/public/SDK/ need to be built in dependency graph order (e.g. Foundation's overlay must be built before AppKit's and so on). This order depends on the current header files in the system. I wrote a tool, utils/find-overlay-dependencies.sh, that uses clang -M to figure out which headers are included by a particular module, but the actual dependencies specified in the CMake files aren't validated in any way.

Since the process of looking for headers by module can be slow, I wouldn't expect it to be something to do on every reconfigure. However, if we could extract the list of dependencies used by CMake for the overlay targets, we could compare it to the dependencies found by the tool. A validation test would be a good way to ensure that these two do not get out of sync.