cmake HAVE_DECL_ISNAN examples

Unidata/netcdf-c CMakeLists.txt :1211 

CHECK_SYMBOL_EXISTS(isnan "math.h" HAVE_DECL_ISNAN)

Kitware/VTK ThirdParty/netcdf/vtknetcdf/CMakeLists.txt :194 

check_symbol_exists("isnan" "math.h" HAVE_DECL_ISNAN)