perf evlist: Add backpointer for perf_env to evlist

Add backpointer to perf_env in evlist, so we can easily access env when
processing something where we have a evsel or evlist.

Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1440755289-30939-5-git-send-email-kan.liang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.h

@@ -56,6 +56,7 @@ struct perf_evlist {
 	struct cpu_map	  *cpus;
 	struct perf_evsel *selected;
 	struct events_stats stats;
+	struct perf_env	*env;
 };
 
 struct perf_evsel_str_handler {

tools/perf/util/header.c

@@ -2514,6 +2514,7 @@ int perf_session__read_header(struct perf_session *session)
 	if (session->evlist == NULL)
 		return -ENOMEM;
 
+	session->evlist->env = &header->env;
 	if (perf_data_file__is_pipe(file))
 		return perf_header__read_pipe(session);