perf version: Append 12 git SHA chars to the version string

perf version: Append 12 git SHA chars to the version string

Bumping it from just 4:

Before:

  $ perf -v
  perf version 5.2.rc1.g80978f
  $

After:

  $ perf -v
  perf version 5.2.rc1.g80978fc864c5
  $

Requested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-p4yun2nxlo7eeeohyx5v4kw7@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>