perf config: Make perf_config_system() global

Make perf_config_system global, it will be used outside the config.c
object in the following patches.

Signed-off-by: Jiri Olsa <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexei Budankov <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Michael Petlan <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/config.c

···
 	return v ? perf_config_bool(k, v) : def;
 }
 
-static int perf_config_system(void)
+int perf_config_system(void)
 {
 	return !perf_env_bool("PERF_CONFIG_NOSYSTEM", 0);
 }

tools/perf/util/config.h

···
 int config_error_nonbool(const char *);
 const char *perf_etc_perfconfig(void);
 const char *perf_home_perfconfig(void);
+int perf_config_system(void);
 
 struct perf_config_set *perf_config_set__new(void);
 struct perf_config_set *perf_config_set__load_file(const char *file);