perf evsel: Fall back to global 'perf_env' in perf_evsel__env()

I.e. if evsel->evlist or evsel->evlist->env isn't set, return the
environment for the running machine, as that would be set if reading
from a perf.data file.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-uqq4grmhbi12rwb0lfpo6lfu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/python.c

@@ -14,6 +14,7 @@
 #include "thread_map.h"
 #include "trace-event.h"
 #include "mmap.h"
+#include "util/env.h"
 #include <internal/lib.h>
 #include "../perf-sys.h"
 
@@ -53,6 +54,11 @@ int parse_callchain_record(const char *arg __maybe_unused,
 	return 0;
 }
 
+/*
+ * Add this one here not to drag util/env.c
+ */
+struct perf_env perf_env;
+
 /*
  * Support debug printing even though util/debug.c is not linked.  That means
  * implementing 'verbose' and 'eprintf'.