[Config] Gracefully handle type mismatches in cvars.

Detect cvar type mismatch and reset to default value, as well
as show message to the user that the cvar from the config has
been updated.

src/xenia/base/cvar.cc

@@ -30,6 +30,7 @@ cxxopts::Options options("xenia", "Xbox 360 Emulator");
 std::map<std::string, ICommandVar*>* CmdVars;
 std::map<std::string, IConfigVar*>* ConfigVars;
 std::multimap<uint32_t, const IConfigVarUpdate*>* IConfigVarUpdate::updates_;
+std::vector<std::string>* config_type_mismatch_warnings = nullptr;
 
 void PrintHelpAndExit() {
   std::cout << options.help({""}) << std::endl;