cmake LIBNSL_HAS_GETHOSTBYADDR examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :460 

check_library_exists(nsl gethostbyaddr "" LIBNSL_HAS_GETHOSTBYADDR)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :463 

else(LIBNSL_HAS_GETHOSTBYADDR)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :470 

endif(LIBNSL_HAS_GETHOSTBYADDR)