perf string: Export asprintf__tp_filter_pids()

perf string: Export asprintf__tp_filter_pids()

Will be used directly in 'perf trace' for setting up the command line
argv array to pass to cmd_record, as this was how 'perf trace record'
was implemented, following the model used in 'perf kvm record', 'perf
sched record', etc.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-w3cuwjs63lxf5zpryy3145uv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>