HPCC-12035 Implement portable j_isnan() and j_isinf() functions

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-12035 Update based on review

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #6316 from afishbeck/windowsIsNaN

HPCC-12035 Implement isnan() and isinf() for windows

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>