merge bitcoin#18914, #13306, #16424, #13899, #17486, #17880, #18145, #18843, #16710: split warnings out of CXXFLAGS, add more flags

[kwvg]

Should take care of this warning generated on macOS Mojave

In file included from qt/moc_signverifymessagedialog.cpp:8:
./qt/signverifymessagedialog.h:36:10: warning: 'eventFilter' overrides a member function but is not marked 'override'
      [-Winconsistent-missing-override]
    bool eventFilter(QObject *object, QEvent *event);
         ^
/Users/localhost/Projects/dash/depends/x86_64-apple-darwin18.7.0/include/QtWidgets/qdialog.h:111:10: note: overridden virtual function is here
    bool eventFilter(QObject *, QEvent *) override;
         ^

[PastaPastaPasta]

Better to backport bitcoin#18914 to avoid merge conflicts

[UdjinM6]

diff --git a/src/qt/qrdialog.h b/src/qt/qrdialog.h
index 46d9cbcb1a..3c503fe1e3 100644
--- a/src/qt/qrdialog.h
+++ b/src/qt/qrdialog.h
@@ -35,8 +35,8 @@ public Q_SLOTS:
     void copyImage();
 
 protected:
-    virtual void mousePressEvent(QMouseEvent *event);
-    virtual void contextMenuEvent(QContextMenuEvent *event);
+    virtual void mousePressEvent(QMouseEvent *event) override;
+    virtual void contextMenuEvent(QContextMenuEvent *event) override;
 
 private:
     QMenu *contextMenu;

[PastaPastaPasta]

utACK

[UdjinM6]

13899 is incomplete but it's fine, can be fixed later (there are quite a few other things to fix when compiled with these new flags)

ACK