...as emitted by at least GCC 8.2 with --enable-optimized.  These are not
actually problems, as in both cases strncpy(p,...,N-1) is used to copy a
string into an area p of length N that has initially been zero-initialized, so
p[N-1] will already contain NUL.  But add the (redundant) p[N-1]=NUL just in
case, and to silence GCC (where the documentation explicitly recommends this
additional write as a way to silence the warning).  Unfortunately, in hstyle.cxx
at least GCC 8.2 with --enable-optimized would still emit the warning, even
though it uses the recommended way of handling it, so needs to be silenced with
a #pragma.

Change-Id: Ie41f420c732c2bfb699903ebd21ce1a89dd2b236
Reviewed-on: https://gerrit.libreoffice.org/66620
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>