perf probe: Fix unchecked usage of strncpy()

perf probe: Fix unchecked usage of strncpy()

The strncpy() function may leave the destination string buffer
unterminated, better use strlcpy() that we have a __weak fallback
implementation for systems without it.

In this case the 'target' buffer is coming from a list of build-ids that
are expected to have a len of at most (SBUILD_ID_SIZE - 1) chars, so
probably we're safe, but since we're using strncpy() here, use strlcpy()
instead to provide the intended safety checking without the using the
problematic strncpy() function.

This fixes this warning on an Alpine Linux Edge system with gcc 8.2:

  util/probe-file.c: In function 'probe_cache__open.isra.5':
  util/probe-file.c:427:3: error: 'strncpy' specified bound 41 equals destination size [-Werror=stringop-truncation]
     strncpy(sbuildid, target, SBUILD_ID_SIZE);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: 1f3736c9c833 ("perf probe: Show all cached probes")
Link: https://lkml.kernel.org/n/tip-l7n8ggc9kl38qtdlouke5yp5@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>