cmake HAVE_PCAP_DUMP_FTELL examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :824 

check_function_exists(pcap_dump_ftell HAVE_PCAP_DUMP_FTELL)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :1423 

endif(NOT HAVE_PCAP_DUMP_FTELL)