perf trace: Avoid early exit due SIGCHLD from non-workload processes

perf trace: Avoid early exit due SIGCHLD from non-workload processes

The function trace__symbols_init() runs "perf-read-vdso32" and that ends up
with a SIGCHLD delivered to 'perf'. And this SIGCHLD make perf exit early.

'perf trace' should exit only if the SIGCHLD is from our workload process.
So let's use sigaction() instead of signal() to match such condition.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.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/20220208140725.3947-1-changbin.du@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>