* Capture reexported libraries, allowable clients, rpaths, shared cache
eligibility.
* Add support for select Xarch options.
* Add diagnostics related to capturing these options.
* Add support for verifying these attributes against what is encoded in
the dylib.
* A lot of `tapi installapi` options are already shared with clang, but
not all. This patch handles installapi-specific options by filtering for
them in the initial argv input, then passing the rest to the clang
driver.
* Installapi not only generates a text file but also reports to library
developers when there are inconsistencies between an interface and its
implementation. To allow this, add support for reporting installapi
diagnostics. This will be leveraged in the verifier service.
