In commit beb991110d (Remove now-unused code once used on IRIX,
2019-01-11, v3.14.0-rc1~167^2) we removed remnants of IRIX support.
Also remove remnants of MIPSpro compiler support.
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.