Setting the `STD_CDEFINES` environment variable before running `configure`

can be used to enable certain compile-time options that are not explicitly

defined in `configure`.

Some of these settings are:

|Setting |Description |

|-----------------------------------|----------------------------------------|

|`-DISC_MEM_FILL=0`|Don't ovewrite memory when allocating or freeing it; this improves performance but makes debugging more difficult.|

|`-DISC_MEM_TRACKLINES=0`|Don't track memory allocations by file and line number; this improves performance but makes debugging more difficult.|

|<nobr>`-DISC_FACILITY=LOG_LOCAL0`</nobr>|Change the default syslog facility for `named`|

|`-DNS_CLIENT_DROPPORT=0`|Disable dropping queries from particular well-known ports:|

|`-DCHECK_SIBLING=0`|Don't check sibling glue in `named-checkzone`|

|`-DCHECK_LOCAL=0`|Don't check out-of-zone addresses in `named-checkzone`|

|`-DNS_RUN_PID_DIR=0`|Create default PID files in `${localstatedir}/run` rather than `${localstatedir}/run/{named,lwresd}/`|

|`-DDIG_SIGCHASE=1`|Enable DNSSEC signature chasing support in `dig`. (Note: This feature is deprecated. Use `delv` instead.)|

|`-DNS_RPZ_MAX_ZONES=64`|Increase the maximum number of configurable response policy zones from 32 to 64; this is the highest possible setting|

|`-DISC_HEAP_CHECK`|Test heap consistency after every heap operation; used when debugging|

|`-DISC_BUFFER_USEINLINE=0`|Disable the use of inline functions to implement the `isc_buffer` API: this reduces performance but may be useful when debugging |