Create setup.h when building wxscintilla library.

Create setup.h when building wxscintilla library.

This library includes some wx headers and so setup.h must be available when
it's being compiled but there was no rule to copy it in its projects, so add
it now.

Closes #13526.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69242 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775