Define wxEntry() with WinMain-compatible signature for all Windows ports.

Make wxEntry(HINSTANCE, ...) available in wxGTK under Windows too.

Refactor the headers to allow this and extract Windows-specific wxEntry()
declarations in wx/msw/init.h from wx/msw/app.h for consistency with the
normal wxEntry(int, char**) declared in wx/init.h.

Closes #14423.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71890 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/init.h

@@ -53,6 +53,12 @@ extern int WXDLLIMPEXP_BASE wxEntry(int& argc, char **argv);
 
 #endif// wxUSE_UNICODE
 
+// Under Windows we define additional wxEntry() overloads with signature
+// compatible with WinMain() and not the traditional main().
+#if wxUSE_GUI && defined(__WINDOWS__)
+    #include "wx/msw/init.h"
+#endif
+
 // ----------------------------------------------------------------------------
 // Using the library without (explicit) application object: you may avoid using
 // wxDECLARE_APP and wxIMPLEMENT_APP macros and call the functions below instead at