Even though we disable warnings when building jsoncpp itself, including
its headers from other CMake sources may still cause warnings.
Additional work will be needed to port CMake to newer jsoncpp interfaces
while still supporting jsoncpp 1.0.0. For now, just suppress the
markup.
Update json/json.h to account for our lack of autolink.h. Update
json/config.h to include KWSys Large File Support configuration so that
consistent stream libraries are used (on AIX with XL).
Add a cm_jsoncpp_reader.h header to include the CMake-provided copy of
the json/reader.h header from CMake sources.
