The python3-setuptools package is needed to build the python binding, so
that one can use things like:

  # ~acme/git/perf/tools/perf/python/twatch.py
  cpu: 6, pid: 4573, tid: 2184618 { type: exit, pid: 4573, ppid: 4172, tid: 2184618, ptid: 4172, time: 12563190090107}
  cpu: 24, pid: 4573, tid: 4573 { type: fork, pid: 4573, ppid: 4573, tid: 2190991e, ptid: 4573, time: 12563415289331}
  cpu: 29, pid: 4573, tid: 2190991e { type: comm, pid: 4573, tid: 2190991e, comm: StreamT~ns #401 }
  cpu: 29, pid: 4573, tid: 2190991e { type: comm, pid: 4573, tid: 2190991e, comm: StreamT~ns #401 }
  ^CTraceback (most recent call last):
    File "/var/home/acme/git/perf/tools/perf/python/twatch.py", line 61, in <module>
      main()
    File "/var/home/acme/git/perf/tools/perf/python/twatch.py", line 33, in main
      evlist.poll(timeout = -1)
  KeyboardInterrupt

  #

That have 'import perf;'.

But distros don't always have that python3-setuptools (or equivalent)
installed, which was breaking the build. Just check if it is installed
and emit a warning that such binding isn't being built and continue the
build without it:

With it:

  $ rpm -q python3-setuptools
  python3-setuptools-59.6.0-3.fc36.noarch
  $ rm -rf /tmp/build/perf; mkdir -p /tmp/build/perf
  $ make O=/tmp/build/perf -C tools/perf install-bin
  make: Entering directory '/var/home/acme/git/perf/tools/perf'
  <SNIP>
  ...                               libpython: [ on  ]
  <SNIP>
    GEN     /tmp/build/perf/python/perf.cpython-310-x86_64-linux-gnu.so
  <SNIP>
  $ ls -la /tmp/build/perf/python/perf.cpython-310-x86_64-linux-gnu.so
  -rwxr-xr-x. 1 acme acme 1609112 Dec 17 11:39 /tmp/build/perf/python/perf.cpython-310-x86_64-linux-gnu.so
  $

Without it:

  $ sudo rpm -e python3-setuptools
  $ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf
  $ make O=/tmp/build/perf -C tools/perf install-bin
  make: Entering directory '/var/home/acme/git/perf/tools/perf'
  <SNIP>
  ...                               libpython: [ on  ]
  <SNIP>
  $ ls -la /tmp/build/perf/python/perf.cpython-310-x86_64-linux-gnu.so
  ls: cannot access '/tmp/build/perf/python/perf.cpython-310-x86_64-linux-gnu.so': No such file or directory
  $
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/Y53XHw3rlsaaUgOs@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>