[PATCH v6 5/9] perf config: Add global variable 'config_set'

The config set is prepared by collecting all configs from config files (i.e. user config ~/.perfconfig and system config $(sysconfdir)/perfconfig) so the config set contains all config key-value pairs. We need to use it as global variable to share it. And in near future, the variable will be

[PATCH v6 5/9] perf config: Add global variable 'config_set'

The config set is prepared by collecting all configs from config files (i.e. user config ~/.perfconfig and system config $(sysconfdir)/perfconfig) so the config set contains all config key-value pairs. We need to use it as global variable to share it. And in near future, the variable will be