ddnsu 0.3.0 installs fine on Mac OS X 10.6.2 Snow Leopard, but 0.3.1 and later fail; here's a build log from 0.3.5:
gcc -Os -Wall -DCONFIGFILE_MODE=1 -DUSE_OPENSSL=1 -DUSE_SYSLOG=1 -DSYSLOG_FACILITY=\"LOG_LOCAL0\" -DPOLLING_MODE=1 -DPOLLING_KEEP_STATE -DDYNDNS_SERVICE=1 -DNOIP_SERVICE=1 -c base64_encode.c
gcc -Os -Wall -DCONFIGFILE_MODE=1 -DUSE_OPENSSL=1 -DUSE_SYSLOG=1 -DSYSLOG_FACILITY=\"LOG_LOCAL0\" -DPOLLING_MODE=1 -DPOLLING_KEEP_STATE -DDYNDNS_SERVICE=1 -DNOIP_SERVICE=1 -c ddnsu.c
ddnsu.c: In function 'skip_http_headers':
ddnsu.c:793: warning: pointer targets in passing argument 2 of 'my_getline' differ in signedness
ddnsu.c: In function 'sock_skip_http_headers':
ddnsu.c:811: warning: pointer targets in passing argument 1 of 'fgets' differ in signedness
ddnsu.c:812: warning: pointer targets in passing argument 1 of 'strip_crlf' differ in signedness
ddnsu.c:817: warning: pointer targets in passing argument 1 of 'strlen' differ in signedness
gcc -Os -Wall -DCONFIGFILE_MODE=1 -DUSE_OPENSSL=1 -DUSE_SYSLOG=1 -DSYSLOG_FACILITY=\"LOG_LOCAL0\" -DPOLLING_MODE=1 -DPOLLING_KEEP_STATE -DDYNDNS_SERVICE=1 -DNOIP_SERVICE=1 -DSYSLOG_FACILITY=LOG_LOCAL0 -c log.c
<command-line>: warning: "SYSLOG_FACILITY" redefined
<command-line>: warning: this is the location of the previous definition
log.c: In function 'log_generic':
log.c:113: warning: format not a string literal and no format arguments
log.c:115: warning: format not a string literal and no format arguments
gcc -Os -Wall -DCONFIGFILE_MODE=1 -DUSE_OPENSSL=1 -DUSE_SYSLOG=1 -DSYSLOG_FACILITY=\"LOG_LOCAL0\" -DPOLLING_MODE=1 -DPOLLING_KEEP_STATE -DDYNDNS_SERVICE=1 -DNOIP_SERVICE=1 -c polling.c
In file included from polling.h:25,
from polling.c:25:
/usr/include/net/if.h:264: error: field 'ifru_addr' has incomplete type
/usr/include/net/if.h:265: error: field 'ifru_dstaddr' has incomplete type
/usr/include/net/if.h:266: error: field 'ifru_broadaddr' has incomplete type
/usr/include/net/if.h:305: error: field 'ifra_addr' has incomplete type
/usr/include/net/if.h:306: error: field 'ifra_broadaddr' has incomplete type
/usr/include/net/if.h:307: error: field 'ifra_mask' has incomplete type
/usr/include/net/if.h:379: error: field 'addr' has incomplete type
/usr/include/net/if.h:380: error: field 'dstaddr' has incomplete type
make: *** [polling.o] Error 1