Disable test for setting the creation time under Unix.

Also document that this doesn't work there.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74424 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Only link with libwxscintilla if using Scintilla is enabled.

Correct the changes of r74408 to avoid using libwxscintilla if we don't build
it at all.

See #13837.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74425 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775