perf session: Change type to avoid undefined behaviour in a signal handler

The 'session_done' variable is written to inside the signal handler of
'perf report' and 'perf script'. Switch its type to avoid undefined
behavior.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20221024181913.630986-6-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/session.c

 // SPDX-License-Identifier: GPL-2.0
 #include <errno.h>
+#include <signal.h>
 #include <inttypes.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
@@ -2022,7 +2023,7 @@ static int perf_session__flush_thread_stacks(struct perf_session *session)
 					 NULL);
 }
 
-volatile int session_done;
+volatile sig_atomic_t session_done;
 
 static int __perf_session__process_decomp_events(struct perf_session *session);