* This patch introduces a container class, for holding records and
attributes only collectible from the clang frontend, which is a subclass
of `llvm::MachO::RecordsSlice`
* This also prunes out collecting declarations from headers that aren't
considered input to installapi.
* Uses these constructs for collecting global objective-c interfaces.
This patch takes in json files as input to determine that header files
to process, and in which order, to pass along for CC1 invocations. This
patch also includes an ASTVisitor to collect simple global variables.