Fix various small warnings (#4296)

* Fix `inconsistent-missing-override` warnings

* Fix `final-dtor-non-final-class` warnings

* Fix `ambiguous-reversed-operator` warnings

src/CMakeLists.txt

@@ -846,6 +846,10 @@ else ()
         target_compile_options(${LIBRARY_PROJECT} PUBLIC
             -Wno-unused-local-typedef
             -Wno-unused-private-field
+            -Werror=inconsistent-missing-override
+            -Werror=final-dtor-non-final-class
+            -Werror=ambiguous-reversed-operator
+
         )
     else ()
         target_compile_options(${LIBRARY_PROJECT} PUBLIC

src/common/FlagsEnum.hpp

@@ -27,12 +27,12 @@ public:
         }
     }
 
-    bool operator==(const FlagsEnum<T> &other)
+    bool operator==(const FlagsEnum<T> &other) const
     {
         return this->value_ == other.value_;
     }
 
-    bool operator!=(const FlagsEnum<T> &other)
+    bool operator!=(const FlagsEnum<T> &other) const
     {
         return this->value_ != other.value_;
     }

src/widgets/dialogs/ColorPickerDialog.hpp

@@ -53,8 +53,8 @@ public:
     pajlada::Signals::Signal<QColor> closed;
 
 protected:
-    void closeEvent(QCloseEvent *);
-    void themeChangedEvent();
+    void closeEvent(QCloseEvent *) override;
+    void themeChangedEvent() override;
 
 private:
     struct {

src/widgets/dialogs/EditHotkeyDialog.hpp

@@ -14,7 +14,7 @@ namespace chatterino {
 
 class Hotkey;
 
-class EditHotkeyDialog : public QDialog
+class EditHotkeyDialog final : public QDialog
 {
     Q_OBJECT