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.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/PERF-VERSION-GEN

@@ -19,7 +19,7 @@ TAG=
 if test -d ../../.git -o -f ../../.git
 then
 	TAG=$(git describe --abbrev=0 --match "v[0-9].[0-9]*" 2>/dev/null )
-	CID=$(git log -1 --abbrev=4 --pretty=format:"%h" 2>/dev/null) && CID="-g$CID"
+	CID=$(git log -1 --abbrev=12 --pretty=format:"%h" 2>/dev/null) && CID="-g$CID"
 elif test -f ../../PERF-VERSION-FILE
 then
 	TAG=$(cut -d' ' -f3 ../../PERF-VERSION-FILE | sed -e 's/\"//g')