Revert "Remove unused variable."

It's only unused on Mac

This reverts commit d3fb22014f.

common/widgets/gal_options_panel.cpp

@@ -66,6 +66,7 @@ static const UTIL::CFG_MAP<KIGFX::GRID_SNAPPING> gridSnapConfigVals =
 
 GAL_OPTIONS_PANEL::GAL_OPTIONS_PANEL( wxWindow* aParent, EDA_DRAW_FRAME* aDrawFrame ) :
     wxPanel( aParent, wxID_ANY ),
+    m_drawFrame( aDrawFrame ),
     m_galOptions( aDrawFrame->GetGalDisplayOptions() )
 {
     // the main sizer that holds "columns" of settings

include/widgets/gal_options_panel.h

@@ -51,6 +51,8 @@ public:
     bool TransferDataFromWindow() override;
 
 private:
+    EDA_DRAW_FRAME*   m_drawFrame;
+
     wxBoxSizer*       m_mainSizer;
 
 #ifndef __WXMAC__