Build failure of FL/platform.H, at FL.cxx (line 22)

[rageworx]

Build log,

In file included from Fl.cxx:22:
../FL/platform.H:68:8: error: ‘Window’ does not name a type; did you mean ‘Fl_Window’?
   68 | inline Window fl_xid(const Fl_Window* w) { Fl_X *xTemp = Fl_X::flx(w); return xTemp ? (Window)xTemp->xid : 0; }
      |        ^~~~~~
      |        Fl_Window
../FL/platform.H:74:29: warning: ‘fl_find’ initialized and declared ‘extern’
   74 | extern FL_EXPORT Fl_Window* fl_find(Window xid);
      |                             ^~~~~~~
../FL/platform.H:74:37: error: ‘Window’ was not declared in this scope
   74 | extern FL_EXPORT Fl_Window* fl_find(Window xid);
      |                                     ^~~~~~
../FL/platform.H:77:18: error: ‘Window’ does not name a type; did you mean ‘Fl_Window’?
   77 | extern FL_EXPORT Window fl_window;
      |                  ^~~~~~
      |                  Fl_Window
Fl.cxx:702:12: error: redefinition of ‘Fl_Window* fl_find’
  702 | Fl_Window* fl_find(Window xid) {
      |            ^~~~~~~
In file included from Fl.cxx:22:
../FL/platform.H:74:29: note: ‘Fl_Window* fl_find’ previously defined here
   74 | extern FL_EXPORT Fl_Window* fl_find(Window xid);
      |                             ^~~~~~~
Fl.cxx:702:20: error: ‘Window’ was not declared in this scope
  702 | Fl_Window* fl_find(Window xid) {
      |                    ^~~~~~
Fl.cxx:2160:11: error: ‘Window’ does not name a type; did you mean ‘Fl_Window’?
 2160 | FL_EXPORT Window fl_xid_(const Fl_Window *w) {
      |           ^~~~~~
      |           Fl_Window

[rageworx]

This issue was solved by using MinGW-W64 g++, not MSYS g++.