cmake HAVE_BPF_DUMP examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :947 

check_function_exists(bpf_dump HAVE_BPF_DUMP)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :1420 

endif(NOT HAVE_BPF_DUMP)