util: Do not use gArgs global in ArgsManager member functions

src/util/system.cpp

@@ -523,7 +523,7 @@ void ArgsManager::AddHiddenArgs(const std::vector<std::string>& names)
 
 std::string ArgsManager::GetHelpMessage() const
 {
-    const bool show_debug = gArgs.GetBoolArg("-help-debug", false);
+    const bool show_debug = GetBoolArg("-help-debug", false);
 
     std::string usage = "";
     LOCK(cs_args);
@@ -900,7 +900,7 @@ bool ArgsManager::ReadConfigFiles(std::string& error, bool ignore_invalid_keys)
     // If datadir is changed in .conf file:
     ClearDatadirCache();
     if (!CheckDataDirOption()) {
-        error = strprintf("specified data directory \"%s\" does not exist.", gArgs.GetArg("-datadir", ""));
+        error = strprintf("specified data directory \"%s\" does not exist.", GetArg("-datadir", ""));
         return false;
     }
     return true;