gcc 8 breaks build

[0-wiz-0]

On NetBSD 9.99.17 with gcc 8, pkgin does not compile:

--- tools.o ---
In file included from /usr/include/string.h:127,
                 from /scratch/pkgtools/pkgin/work/libnbcompat/nbcompat/string.h:36,
                 from /scratch/pkgtools/pkgin/work/libnbcompat/nbcompat.h:62,
                 from tools.h:37,
                 from tools.c:30:
tools.c: In function 'strreplace':
tools.c:170:4: error: '__builtin___strncat_chk' output truncated before terminating nul copying as many bytes from a string as its length [-Werror=str
ingop-truncation]
    strncat(buf, to, tolen);
    ^~~~~~~
tools.c:166:10: note: length computed here
  tolen = strlen(to);
          ^~~~~~~~~~

Please fix :)
Thanks.