perf tools: Fix empty version number when building outside of a git repo

perf tools: Fix empty version number when building outside of a git repo

When perf is built in a full source tree that is not a git repository,
e.g. from a kernel source tarball, `perf version` will print empty tag
and commit strings:

  $ perf version
  perf version

Currently the tag version is only generated from the root Makefile when
building in a git repository. If PERF-VERSION-FILE has not been
generated and the source tree is not in a git repository, then
PERF-VERSION-GEN will return an empty version.

The problem can be reproduced with the following steps:

  $ wget https://git.kernel.org/torvalds/t/linux-6.0-rc7.tar.gz
  $ tar -xf linux-6.0-rc7.tar.gz && cd linux-6.0-rc7
  $ make -C tools/perf
  $ tools/perf/perf -v
  perf version

Builds from tarballs generated with `make perf-tar-src-pkg` are not
impacted by this issue as PERF-VERSION-FILE is included in the archive.

The perf RPM provided by Fedora for 5.18+ is experiencing this problem.
Package build logs[0] show that the build is attempting to fall back on
PERF-VERSION-FILE, but it is not present.

To resolve this, revert back to the previous logic of using the kernel
Makefile version if not in a git repository and PERF-VERSION-FILE does
not exist.

[0] https://kojipkgs.fedoraproject.org/packages/kernel-tools/5.19.4/200.fc36/data/logs/x86_64/build.log

Fixes: 7572733b84997d23 ("perf tools: Fix version kernel tag")
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Will Chandler <wfc@wfchandler.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220930151157.529674-1-wfc@wfchandler.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>