klaus,
after editing my debian/rules i managed to compile nathelper in verbose mode and didn't get any warnings:
make[2]: Entering directory `/usr/src/trunk-src/openxg-sip-proxy/modules_k/nathelper' gcc -fPIC -DPIC -g -O2 -DNAME='"sip-proxy"' -DVERSION='"2.99.99-pre3"' -DARCH='"i386"' -DOS='linux_' -DOS_QUOTED='"linux"' -DCOMPILER='"gcc 4.3.2"' -D__CPU_i386 -D__OS_linux -DSER_VER=2099099 -DCFG_DIR='"/etc/sip-proxy/"' -DPKG_MALLOC -DSHM_MEM -DSHM_MMAP -DDNS_IP_HACK -DUSE_MCAST -DUSE_TCP -DDISABLE_NAGLE -DHAVE_RESOLV_RES -DUSE_DNS_CACHE -DUSE_DNS_FAILOVER -DUSE_DST_BLACKLIST -DUSE_NAPTR -DF_MALLOC -DUSE_TLS -DTLS_HOOKS -DSTATISTICS -DFAST_LOCK -DADAPTIVE_WAIT -DADAPTIVE_WAIT_LOOPS=1024 -DCC_GCC_LIKE_ASM -DHAVE_GETHOSTBYNAME2 -DHAVE_UNION_SEMUN -DHAVE_SCHED_YIELD -DHAVE_MSG_NOSIGNAL -DHAVE_MSGHDR_MSG_CONTROL -DHAVE_ALLOCA_H -DHAVE_TIMEGM -DHAVE_SCHED_SETSCHEDULER -DHAVE_EPOLL -DHAVE_SIGIO_RT -DSIGINFO64_WORKARROUND -DUSE_FUTEX -DHAVE_SELECT -DUSE_SCTP -DOPENSER_MOD_INTERFACE -DMOD_NAME='"nathelper"' -c nathelper.c -o nathelper.o
i think you got the warnings from the test version that i emailed to you privately. causes of the warnings have since then been fixed in the git version.
-- juha