cmake HAVE_VSYSLOG examples

CTSRD-CHERI/cheribsd contrib/libpcap/CMakeLists.txt :756 

check_function_exists(vsyslog HAVE_VSYSLOG)

asset-group/5ghoul-5g-nr-attacks libs/libpcap/CMakeLists.txt :465 

check_function_exists(vsyslog HAVE_VSYSLOG)