illumos gate

Build errors on SPARC with gcc 10:

    daemon.c: In function 'anynet_ntoa':
    daemon.c:4369:8: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
     4369 |  *--bp = '\0';
          |  ~~~~~~^~~~~~
    daemon.c:4314:14: note: at offset -1 to object 'buf' with size 100 declared here
     4314 |  static char buf[100];
          |              ^~~
    cc1: all warnings being treated as errors
    *** Error code 1
    dmake: Fatal error: Command failed for target `daemon.o'
    Current working directory /code/illumos-gate/usr/src/cmd/sendmail/src

This error is trying to tell us, we have potential write past array end. I'm not exactly sure why we do not get this on x86 (gcc 10.1 on sparc and 10.2 on x86). Patch is result of iteration with upstream.

Testing done: build is ok.