Provide trivial GDK_IS_X11_DISPLAY() definition for GTK+2.

This will be useful for upcoming patches using it to fix problems with GTK+ 3
without breaking GTK+ 2 compilation.

See #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78157 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't defer wxTLW initialization in wxGTK when not using X11.

See #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78158 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't use frame extents when not using X11 in wxGTK.

See #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78159 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't crash when switching to full screen in non X11-based wxGTK.

Only use internal X11 display if we're running in a such environment.

See #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78160 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't use X11-only functions when not using X11 in wxGTK.

See #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78161 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Credit Marco Trevisan for wxGTK3/Mir patches.

Closes #16688.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78162 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775