core: Make variable shadowing a compile-time error

Now that we have most of core free of shadowing, we can enable the
warning as an error to catch anything that may be remaining and also
eliminate this class of logic bug entirely.

src/core/hle/kernel/k_scheduler.h

@@ -30,7 +30,7 @@ class KThread;
 
 class KScheduler final {
 public:
-    explicit KScheduler(Core::System& system, s32 core_id);
+    explicit KScheduler(Core::System& system_, s32 core_id_);
     ~KScheduler();
 
     /// Reschedules to the next available thread (call after current thread is suspended)