In pipe mode, no need to switch perf data output, therefore,
'--timestamp-filename' option should not take effect.
Check the conflict before recording and output WARNING.
In this case, the check pipe mode in perf_data__switch() can be removed.

Before:

  # perf record --timestamp-filename -o- perf test -w noploop | perf report -i- --percent-limit=1
  # To display the perf.data header info, please use --header/--header-only options.
  #
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Dump -.2024011812110182 ]
  #
  # Total Lost Samples: 0
  #
  # Samples: 4K of event 'cycles:P'
  # Event count (approx.): 2176784359
  #
  # Overhead  Command  Shared Object         Symbol
  # ........  .......  ....................  ......................................
  #
      97.83%  perf     perf                  [.] noploop

  #
  # (Tip: Print event counts in CSV format with: perf stat -x,)
  #

After:

  # perf record --timestamp-filename -o- perf test -w noploop | perf report -i- --percent-limit=1
  WARNING: --timestamp-filename option is not available in pipe mode.
  # To display the perf.data header info, please use --header/--header-only options.
  #
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.000 MB - ]
  #
  # Total Lost Samples: 0
  #
  # Samples: 4K of event 'cycles:P'
  # Event count (approx.): 2185575421
  #
  # Overhead  Command  Shared Object          Symbol
  # ........  .......  .....................  .............................................
  #
      97.75%  perf     perf                   [.] noploop

  #
  # (Tip: Profiling branch (mis)predictions with: perf record -b / perf report)
  #

Fixes: ecfd7a9c ("perf record: Add '--timestamp-filename' option to append timestamp to output file name")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240119040304.3708522-3-yangjihong1@huawei.comSigned-off-by: Namhyung Kim <namhyung@kernel.org>