lib/tool/checksum.c fails to compile with -O3

When configuring and compiling with -O3 in CFLAGS, there are compilation errors.

$ ./configure CFLAGS=-O3
$ make -k
make all-am
make[1]: Entering directory `/home/biurrun/src/hipl/trunk'
  CC lib/tool/checksum.lo
cc1: warnings being treated as errors
lib/tool/checksum.c: In function ‘ipv6_checksum’:
lib/tool/checksum.c:196: error: array subscript is above array bounds
make[1]: *** [lib/tool/checksum.lo] Error 1
  CC hipd/hadb.o
cc1: warnings being treated as errors
In file included from /usr/include/string.h:642,
                 from hipd/hadb.c:65:
In function ‘memset’,
    inlined from ‘lsi_assigned’ at hipd/hadb.c:1388,
    inlined from ‘hip_generate_peer_lsi’ at hipd/hadb.c:1448:
/usr/include/bits/string3.h:86: error: call to __builtin___memset_chk will always overflow destination buffer
make[1]: *** [hipd/hadb.o] Error 1
make[1]: Target `all-am' not remade because of errors.
make[1]: Leaving directory `/home/biurrun/src/hipl/trunk'
make: *** [all] Error 2