Add capstone and cubit to the superbuild

Capstone and Cubit are closed-source projects. As such, this MR allows
a user to point to an external Capstone or Cubit instance for use by
consuming applications in the superbuild. Additionally, Kitware
developers who have access to Kitware's internal shared storage  can
pull these projects automatically for the internal development of dependent
applications.
Status Job ID Name Coverage
  External
passed cdash

pending cmb@master-junction-osx-shared-release+superbuild
failed cmb@master-kerbin-windows-shared-release+protobuf+superbuild

00:56:00

failed cmb@master-kerbin-windows-shared-release+superbuild

01:30:39

failed cmb@master-moho-linux-shared-relwithdebinfo+python3+superbuild

00:47:19

failed cmb@master-moho-linux-shared-relwithdebinfo+superbuild

00:52:32

failed cmb@master-norkit-osx-shared-release+superbuild

02:05:33

failed cmb@master-praxis-windows-shared-release+superbuild

01:56:03

failed cmb@master-talosiv-osx-shared-release+superbuild

01:01:39

failed cmb@master-tatooine-osx-shared-release+superbuild

01:21:29

passed ghostflow-branch-check-master

pending smtk@master-junction-osx-shared-release+superbuild
failed smtk@master-kerbin-windows-shared-release+superbuild

01:27:56

failed smtk@master-moho-linux-shared-relwithdebinfo+python3+superbuild

00:39:28

failed smtk@master-moho-linux-shared-relwithdebinfo+superbuild

00:40:45

failed smtk@master-moho-linux-shared-relwithdebinfo+superbuild+vtk

00:26:48

passed smtk@master-norkit-osx-shared-release+superbuild

01:46:51

failed smtk@master-praxis-windows-shared-release+superbuild

01:31:06

passed smtk@master-talosiv-osx-shared-release+superbuild

01:05:54

failed smtk@master-tatooine-osx-shared-release+superbuild

01:00:07