cmake HAVE_DECL__ISNAN examples

Geocld/PeaSyo third-party/json-c/CMakeLists.txt :156 

check_symbol_exists(_isnan          "float.h" HAVE_DECL__ISNAN)

ByConity/ByConity contrib/jsonc-cmake/CMakeLists.txt :166 

check_symbol_exists(_isnan          "float.h" HAVE_DECL__ISNAN)