Add a module to provide the Kitware Information Macro Library (KWIML).
For now always use a bundled copy of the KWIML source.  An option to
use a system-installed KWIML can be added later.

KWIML provides macros for information about fundamental types
(existence, size, signedness, format macros, etc.) without using any
try_compile tests.  VTK will be able to use these macros to enable
multi-architecture builds on some platforms.  We should also be able to
eliminate some try_compile tests to speed up initial configuration.