cmake HAVE_AF_INET6 examples

fluent/fluent-bit lib/c-ares-1.34.4/CMakeLists.txt :393 

CHECK_SYMBOL_EXISTS (AF_INET6        "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_AF_INET6)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :732 

check_symbol_exists(AF_INET6 "sys/types.h;ws2tcpip.h" HAVE_AF_INET6)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :735 

check_symbol_exists(AF_INET6 "sys/types.h;sys/socket.h;netinet/in.h" HAVE_AF_INET6)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :741 

endif(HAVE_AF_INET6 AND HAVE_STRUCT_IN6_ADDR)