cmake HAVE_TCP_KEEPCNT examples

htcondor/htcondor build/cmake/CondorConfigure.cmake :343 

check_symbol_exists(TCP_KEEPCNT "sys/types.h;sys/socket.h;netinet/tcp.h" HAVE_TCP_KEEPCNT)

syslog-ng/syslog-ng CMakeLists.txt :146 

check_symbol_exists(TCP_KEEPCNT   "sys/socket.h;netinet/in.h;netinet/tcp.h" HAVE_TCP_KEEPCNT)