cmake LIBSOCKET_HAS_GETSERVENT examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :488 

check_function_exists(getservent LIBSOCKET_HAS_GETSERVENT)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :492 

endif(LIBSOCKET_HAS_GETSERVENT)