swift234

API notes: Add a CMake option to build the compiled API notes files from YAML sources.

Introduce a new off-by-default CMake option, SWIFT_BUILD_API_NOTES,
which compiles the YAML sources for API notes into the binary form
installed alongside the overlays. This will be the default mode,
replacing KnownObjCMethods.def, shortly.

The new apinotes/ subdirectory contains the translated contents of
KnownObjCMethods.def, courtesy of Anna. It still requires some
revision.

Swift SVN r20370