cmake HAVE_LIBCAP_NG examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :1055 

check_library_exists(cap-ng capng_change_id "" HAVE_LIBCAP_NG)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :1058 

endif(HAVE_LIBCAP_NG)