cmake LIBNSL_HAS_GETRPCBYNUMBER examples

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :579 

check_function_exists(getrpcbynumber LIBNSL_HAS_GETRPCBYNUMBER)

CTSRD-CHERI/cheribsd contrib/tcpdump/CMakeLists.txt :583 

endif(LIBNSL_HAS_GETRPCBYNUMBER)