perf inject: Keep build-ID data if no option is used

perf inject: Keep build-ID data if no option is used

The keep_feat() determines which header features will be kept or
discarded.  Usually 'perf inject' will add build-IDs based on -b, -B or
other related options.  But it lose build-ID when none of those options
are used.  This is meaningful only when --buildid-mmap is not used.

The following example shows the impact of this change.

  $ perf record --no-buildid-mmap true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.037 MB perf.data (5 samples) ]

  $ perf inject -i perf.data -o perf.data.inject

  $ perf buildid-list -i perf.data
  08cccc2a9388d5247ccb3e864f3063b975b0a15d /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
  fd5c4d5673256cd6bda51725dba048dabb0f854e [kernel.kallsyms]
  97a36ce1140071be5c36b147fa0bed173e05a602 [vdso]

  $ perf buildid-list -i perf.data.inject
  97a36ce1140071be5c36b147fa0bed173e05a602 [vdso]

With this change, perf.data.inject would show the same list (of course,
you need to run perf inject again).

Reported-by: Gabriel Marin <gmx@google.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>