Included wx/brush header to complete compilation.

[ronilazzari]

On Fedora 35, either using g++ or clang++, I can only completely compile and build your software if I include wx/brush header in some of your files; otherwise I get these kind of compile errors:

/home/roni/psp/PSP/Project/Exponential.cpp: In member function ‘virtual void Exponential::DrawDC(wxPoint2DDouble, double, wxGraphicsContext*) const’:
/home/roni/psp/PSP/Project/Exponential.cpp:78:59: error: invalid use of incomplete type ‘class wxBrush’
   78 |         gc->SetBrush(wxBrush(m_selectionColour.GetDcRGBA()));
      |                                                           ^
In file included from /usr/include/wx-3.1/wx/event.h:21,
                 from /usr/include/wx-3.1/wx/window.h:18,
                 from /usr/include/wx-3.1/wx/nonownedwnd.h:14,
                 from /usr/include/wx-3.1/wx/toplevel.h:20,
                 from /usr/include/wx-3.1/wx/dialog.h:14,
                 from /usr/include/wx-3.1/wx/msgdlg.h:18,
                 from /home/roni/psp/PSP/Project/Element.h:21,
                 from /home/roni/psp/PSP/Project/ControlElement.h:21,
                 from /home/roni/psp/PSP/Project/Exponential.h:21,
                 from /home/roni/psp/PSP/Project/Exponential.cpp:18:
/usr/include/wx-3.1/wx/gdicmn.h:30:28: note: forward declaration of ‘class wxBrush’
   30 | class WXDLLIMPEXP_FWD_CORE wxBrush;
      |                            ^~~~~~~
/home/roni/psp/PSP/Project/Exponential.cpp:111:48: error: invalid use of incomplete type ‘class wxBrush’
  111 |     gc->SetBrush(wxBrush(wxColour(0, 0, 0, 255)));
      |                                                ^
In file included from /usr/include/wx-3.1/wx/event.h:21,
                 from /usr/include/wx-3.1/wx/window.h:18,
                 from /usr/include/wx-3.1/wx/nonownedwnd.h:14,
                 from /usr/include/wx-3.1/wx/toplevel.h:20,
                 from /usr/include/wx-3.1/wx/dialog.h:14,
                 from /usr/include/wx-3.1/wx/msgdlg.h:18,
                 from /home/roni/psp/PSP/Project/Element.h:21,
                 from /home/roni/psp/PSP/Project/ControlElement.h:21,
                 from /home/roni/psp/PSP/Project/Exponential.h:21,
                 from /home/roni/psp/PSP/Project/Exponential.cpp:18:
/usr/include/wx-3.1/wx/gdicmn.h:30:28: note: forward declaration of ‘class wxBrush’
   30 | class WXDLLIMPEXP_FWD_CORE wxBrush;
      |                            ^~~~~~~
make[2]: *** [CMakeFiles/PSP-UFU.dir/build.make:524: CMakeFiles/PSP-UFU.dir/Project/Exponential.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/PSP-UFU.dir/all] Error 2
make: *** [Makefile:91: all] Error 2

I find it funny that your compilers in your build environments do not complain about that, whereas both g++ (11.2.1) and clang++ (13.0.0) in Fedora 35 do complain about it. Why are my compilers less permissive?

But, in the end, it compiles and runs :-P